Sondersammelgebiets-Volltexte
Refine
Year of publication
Document Type
- Article (8024)
- Part of Periodical (2975)
- Review (207)
- Book (191)
- Report (43)
- Working Paper (34)
- Part of a Book (23)
- Conference Proceeding (19)
- Other (13)
- Diploma Thesis (7)
Language
Has Fulltext
- yes (11559) (remove)
Is part of the Bibliography
- no (11559)
Keywords
- taxonomy (741)
- new species (443)
- morphology (161)
- distribution (125)
- biodiversity (110)
- Odonata (84)
- systematics (80)
- Pflanzengesellschaften (67)
- phylogeny (67)
- new records (59)
Institute
- Biowissenschaften (378)
- Extern (375)
- Institut für Ökologie, Evolution und Diversität (150)
- Senckenbergische Naturforschende Gesellschaft (139)
- Biochemie und Chemie (122)
- Medizin (114)
- Biodiversität und Klima Forschungszentrum (BiK-F) (104)
- Frankfurt Institute for Advanced Studies (FIAS) (45)
- Pharmazie (35)
- Exzellenzcluster Makromolekulare Komplexe (32)
Polyploidy is common in higher eukaryotes, especially in plants, but it is generally assumed that most prokaryotes contain a single copy of a circular chromosome and are therefore monoploid. We have used two independent methods to determine the genome copy number in halophilic archaea, 1) cell lysis in agarose blocks and Southern blot analysis, and 2) Real-Time quantitative PCR. Fast growing H. salinarum cells contain on average about 25 copies of the chromosome in exponential phase, and their ploidy is downregulated to 15 copies in early stationary phase. The chromosome copy number is identical in cultures with a twofold lower growth rate, in contrast to the results reported for several other prokaryotic species. Of three additional replicons of H. salinarum, two have a low copy number that is not growth-phase regulated, while one replicon even shows a higher degree of growth phase-dependent regulation than the main replicon. The genome copy number of H. volcanii is similarly high during exponential phase (on average 18 copies/cell), and it is also downregulated (to 10 copies) as the cells enter stationary phase. The variation of genome copy numbers in the population was addressed by fluorescence microscopy and by FACS analysis. These methods allowed us to verify the growth phase-dependent regulation of ploidy in H. salinarum, and they revealed that there is a wide variation in genome copy numbers in individual cells that is much larger in exponential than in stationary phase. Our results indicate that polyploidy might be more widespread in archaea (or even prokaryotes in general) than previously assumed. Moreover, the presence of so many genome copies in a prokaryote raises questions about the evolutionary significance of this strategy.
Background Olfactory receptors work at the interface between the chemical world of volatile molecules and the perception of scent in the brain. Their main purpose is to translate chemical space into information that can be processed by neural circuits. Assuming that these receptors have evolved to cope with this task, the analysis of their coding strategy promises to yield valuable insight in how to encode chemical information in an efficient way. Results We mimicked olfactory coding by modeling responses of primary olfactory neurons to small molecules using a large set of physicochemical molecular descriptors and artificial neural networks. We then tested these models by recording in vivo receptor neuron responses to a new set of odorants and successfully predicted the responses of five out of seven receptor neurons. Correlation coefficients ranged from 0.66 to 0.85, demonstrating the applicability of our approach for the analysis of olfactory receptor activation data. The molecular descriptors that are best-suited for response prediction vary for different receptor neurons, implying that each receptor neuron detects a different aspect of chemical space. Finally, we demonstrate that receptor responses themselves can be used as descriptors in a predictive model of neuron activation. Conclusions The chemical meaning of molecular descriptors helps understand structure-response relationships for olfactory receptors and their 'receptive fields'. Moreover, it is possible to predict receptor neuron activation from chemical structure using machine-learning techniques, although this is still complicated by a lack of training data.
Background Identification and evaluation of surface binding-pockets and occluded cavities are initial steps in protein structure-based drug design. Characterizing the active site's shape as well as the distribution of surrounding residues plays an important role for a variety of applications such as automated ligand docking or in situ modeling. Comparing the shape similarity of binding site geometries of related proteins provides further insights into the mechanisms of ligand binding. Results We present PocketPicker, an automated grid-based technique for the prediction of protein binding pockets that specifies the shape of a potential binding-site with regard to its buriedness. The method was applied to a representative set of protein-ligand complexes and their corresponding apo-protein structures to evaluate the quality of binding-site predictions. The performance of the pocket detection routine was compared to results achieved with the existing methods CAST, LIGSITE, LIGSITEcs, PASS and SURFNET. Success rates PocketPicker were comparable to those of LIGSITEcs and outperformed the other tools. We introduce a descriptor that translates the arrangement of grid points delineating a detected binding-site into a correlation vector. We show that this shape descriptor is suited for comparative analyses of similar binding-site geometry by examining induced-fit phenomena in aldose reductase. This new method uses information derived from calculations of the buriedness of potential binding-sites. Conclusions The pocket prediction routine of PocketPicker is a useful tool for identification of potential protein binding-pockets. It produces a convenient representation of binding-site shapes including an intuitive description of their accessibility. The shape-descriptor for automated classification of binding-site geometries can be used as an additional tool complementing elaborate manual inspections.
Background The connection of the variable part of the heavy chain (VH) and and the variable part of the light chain (VL) by a peptide linker to form a consecutive polypeptide chain (single chain antibody, scFv) was a breakthrough for the functional production of antibody fragments in Escherichia coli. Being double the size of fragment variable (Fv) fragments and requiring assembly of two independent polypeptide chains, functional Fab fragments are usually produced with significantly lower yields in E. coli. An antibody design combining stability and assay compatibility of the fragment antigen binding (Fab) with high level bacterial expression of single chain Fv fragments would be desirable. The desired antibody fragment should be both suitable for expression as soluble antibody in E. coli and antibody phage display. Results Here, we demonstrate that the introduction of a polypeptide linker between the fragment difficult (Fd) and the light chain (LC), resulting in the formation of a single chain Fab fragment (scFab), can lead to improved production of functional molecules. We tested the impact of various linker designs and modifications of the constant regions on both phage display efficiency and the yield of soluble antibody fragments. A scFab variant without cysteins (scFabdeltaC) connecting the constant part 1 of the heavy chain (CH1) and the constant part of the light chain (CL) were best suited for phage display and production of soluble antibody fragments. Beside the expression system E.coli, the new antibody format was also expressed in Pichia pastoris. Monovalent and divalent fragments (DiFabodies) as well as multimers were characterised. Conclusion A new antibody design offers the generation of bivalent Fab derivates for antibody phage display and production of soluble antibody fragments. This antibody format is of particular value for high throughput proteome binder generation projects, due to the avidity effect and the possible use of common standard sera for detection.
Background The Radical Pair model proposes that magnetoreception is a light-dependent process. Under low monochromatic light from the short-wavelength part of the visual spectrum, migratory birds show orientation in their migratory direction. Under monochromatic light of higher intensity, however, they showed unusual preferences in other directions or axial preferences. To determine whether or not these responses are still controlled by the respective light regimes, European robins, Erithacus rubecula, were tested under UV, Blue, Turquoise and Green light at increasing intensities, with orientation in migratory direction serving as a criterion whether or not magnetoreception works in the normal way. Results Under low light with a quantal flux of 8 times 10 to 15 power quanta s-1 m-2, the birds were well oriented in their seasonally appropriate migratory direction under 424 nm Blue, 502 nm Turquoise and 565 nm Green light, indicating unimpaired magnetoreception. Under 373 nm UV of the same quantal flux, they were not oriented in migratory direction, showing a preference of the east-west axis instead, but they showed excellent orientation in migratory direction under UV of lower intensity. Intensities of above 36 times 10 to 15 power quanta s-1 m-2 of Blue, Turquoise and Green light elicited a variety of responses: disorientation, headings along the east-west axis, headings along the north-south axis or 'fixed' direction tendencies. These responses changed as the intensity was increased from 36 times 10 to the 15 power quanta s-1 m-2 to 54 and 72 times 10 to 15 power quanta s-1 m-2. Conclusion The specific manifestation of responses in directions other than migratory direction clearly depends on the ambient light regime. This implies that although mechanisms normally providing magnetic compass information seem disrupted, processes that are activated by light still control the behavior. It suggests complex interactions between different types of receptors, magnetic and visual. The nature of the receptors involved and details of their connections are not yet known; however, a role of the color cones in the processes mediating magnetic input is suggested.
Oral presentations Background: We selected peptide ligands for the HIV-1 packaging signal PSI by screening phage displayed peptide libraries. Peptide ligands were optimized by screening spot synthesis peptide membranes. The aim of this study is the functional characterization of these peptide ligands with respect to inhibition of HIV-1 replication. Methods: Phage displayed peptide libraries were screened with PSI-RNA structures. The Trp-rich peptide motifs were optimized for specific binding on spot synthesis peptide membranes. The best binding peptide was expressed intracellularly in fusion with RFP or linked to a protein transduction domain (PTD) for intracellular delivery. The effects on virion production were analyzed using pseudotyped lentiviral particles. Results: After positive and negative selection rounds, phages binding specifically to PSI-RNA were identified by ELISA. Peptide inserts contained conserved motifs of aromatic amino acids known to be implicated in binding of PSI-RNA by the natural Gag ligand. The filter assay identified HKWPWW as the best binding ligand for PSI-RNA, which is delivered into several cell lines by addition of a PTD. Compared to a control peptide, the HKWPWW peptide inhibited HIV-1 replication as deduced from reduced titers of culture supernatants. As HKWPWW also binds to the TAR-RNA like the natural nucleocapsid PSI-RNA ligand, the effect on Tat-TAR inhibition will also be analyzed. Currently T-cell lines are established which stably express HKWPWW as well as a control peptide, which will be infected with HIV-1 to monitor the ability of HKWPWW to inhibit wild type HIV-1 replication. Conclusion: The selection of a peptide ligand for PSI-RNA able to inhibit HIV-1 replication proves the suitability of the phage display technology for the selection of peptides binding to RNA-structures. This enables the indentification of peptides serving as leads to interfere with additional targets in the HIV-1 replication cycle.
In an effort to link quantitative morphometric information with molecular data on the population level, we have analysed 19 populations of the conchologically variable land snail Candidula unifasciata from across the species range for variation in quantitative shell traits and at the mitochondrial 16S ribosomal (r)DNA locus. In genetic analysis, including 21 additional populations, we observed two fundamental haplotype clades with an average pairwise sequence divergence of 0.209 ± 0.009 between clades compared to 0.017 ± 0.012 within clades, suggesting the presence of two different evolutionary lineages. Integrating additional shell material from the Senckenberg Malacological Collection, a highly significant discriminant analysis on the morphological shell traits with fundamental haplotype clades as grouping variable suggested that the less frequent haplotype corresponds to the described subspecies C. u. rugosiuscula, which we propose to regard as a distinct species. Both taxa were highly subdivided genetically (FST = 0.648 and 0.777 P < 0.001). This was contrasted by the partition of morphological variance, where only 29.6% and 21.9% of the variance were distributed among populations, respectively. In C. unifasciata, no significant association between population pairwise FST estimates and corresponding morphological fixation indices could be detected, indicating independent evolution of the two character sets. Partial least square analysis of environmental factors against shell trait variables in C. u. unifasciata revealed significant correlations between environmental factors and certain quantitative shell traits, whose potential adaptational values are discussed.
Ribosomal proteins are assumed to stabilize specific RNA structures and promote compact folding of the large rRNA. The conformational dynamics of the protein between the bound and unbound state play an important role in the binding process. We have studied those dynamical changes in detail for the highly conserved complex between the ribosomal protein L11 and the GTPase region of 23S rRNA. The RNA domain is compactly folded into a well defined tertiary structure, which is further stabilized by the association with the C-terminal domain of the L11 protein (L11ctd). In addition, the N-terminal domain of L11 (L11ntd) is implicated in the binding of the natural thiazole antibiotic thiostrepton, which disrupts the elongation factor function. We have studied the conformation of the ribosomal protein and its dynamics by NMR in the unbound state, the RNA bound state and in the ternary complex with the RNA and thiostrepton. Our data reveal a rearrangement of the L11ntd, placing it closer to the RNA after binding of thiostrepton, which may prevent binding of elongation factors. We propose a model for the ternary L11–RNA–thiostrepton complex that is additionally based on interaction data and conformational information of the L11 protein. The model is consistent with earlier findings and provides an explanation for the role of L11ntd in elongation factor binding.
In the inundation area - the basin of the former larger Lake Chad - a special type of sorghum is grown on the clay soils (firgi). This dry-season guinea corn is also called dwarf sorghum or masakwa. In Kanuri, the dominant language in the region, sorghum is called ngawuli. The dry-season types are called ngawuli firgibe (lit. translated: sorghum of the firgi). During the dry season when the natural vegetation becomes dry and yellow, masakwa fields appear in prominent green covering large areas of the clay plains. The most important natural factor for this specialized dry season cropping is the presence of soils with a high clay content. For a better understanding of masakwa and its related issues, a multidisciplinary sub-project (G1) has been established within the SFB 268 (Joint Research Project: History of Culture and Language in the Natural Environment of the West-African Savannah). This project in which all disciplines participate is entitled: "Natural basis for masakwa cultivation and its meaning for the settlement history of the clay plains (firgi) in the Chad basin".
Während über Flora und Vegetation der Wälder, Savannen und Äcker Westafrikas zahlreiche Veröffentlichungen vorliegen, hat man sich mit der ruderalen Flora und Vegetation der Siedlungen bisher nur wenig beschäftigt. Im Rahmen der Forschungen des SFB 268 wurde daher in zwei Ortschaften von Burkina Faso eine Bestandsaufnahme der spontan im Siedlungsbereich und in seiner engeren Umgebung an Ruderalstandorten auftretenden Pflanzenarten durchgeführt, wobei, gemäß den Zielen des SFB 268, auf eine interdisziplinäre Relevanz der Ergebnisse Wert gelegt wurde. Daher standen die Fragen nach der Nutzung der Spontanflora durch die Bevölkerung im Vordergrund des Interesses. In der vorliegenden Arbeit wird über die für die menschliche Ernährung genutzten krautigen Wildpflanzen des Siedlungsbereiches berichtet.
The investigations carried out within the project in NE-Nigeria since 1989 have been focussing on the late Pleistocene and Holocene landscape development of the south eastern Chad basin. Areas of interest include palaeodune fields, clay plains and former beach ridge systems of Lake Chad. Transgressions and regressions of Lake Chad played an important role in the younger landscape history of NE-Nigeria and have also caused great environmental changes. The term „Megachad“ is well known and describes an enormous lake with an extension comparable with the Caspian Sea of today. The term „Microchad“ stands for the other recent extreme in terms of the lake dimensions varying during the times. Environmental changes in the surroundings of Lake Chad are closely connected with transgressions and regressions of the lake. These lake level changes can be climatically induced as well as non-climatically, due to human impact. Nearly all land units have more or less been influenced by the lake, spatially as well as temporally. It is important, though, to notice the scales of the changes. Some changes took place in a millennial scale, some in the scales of centuries or decades, and at least – as can be observed every year – in a seasonal scale.
Numerous ecologists postulate that West African savannas are mostly the result of degradation of formerly closed forests. This hypothesis can only be tested by palaeoecological investigations. The palynological results summarised in this paper document the history of the Sudanian and Sahelian savanna of NE-Nigeria during the last 11.500 years (uncal. BP). Both sites investigated provide evidence for the persistence of savanna throughout the entire Holocene. Patches of closed dry forest may have occurred, but never completely displaced the savanna vegetation. Humid conditions during the early and mid Holocene (from 10.000 BP onwards) caused a rapid spread of Guinean and Sudanian taxa into the northern vegetation zones. A slow return to drier climatic conditions between ca. 6800 BP and ca. 5500 BP can be recorded at both sites. Finally, between 3800 BP and 3300 BP a strong aridification resulted in the establishment of the modern vegetation zones. In both the Sahelian and Sudanian zone the vegetational changes appear to have been primarily controlled by climatic changes, whereas the effects of human activities remain palynologically silent even for the late Holocene.
Two sites situated in the Sahelian and Sudanian zones of NE-Nigeria were chosen for pollen analysis. A sediment core from an interdunal depression in the eastern Manga Grassland provides information on the Holocene vegetation history of the Sahel between c. 9600-3400 B.P. The 3 m pollen record indicates an open savanna during the mid-Holocene. The presence of Sudano-Guinean taxa, which were mainly restricted to the interdunal depressions, points to more humid conditions. Already before c. 4000 B.P., a slow change towards drier conditions and the establishment of the modern Sahelian vegetation is visible in the diagram. This development was accompanied by high fire frequencies. A 16 m core from a crater lake (Lake Tilla) in the Sudanian zone of NE-Nigeria provides a pollen record which can be dated back to approximately 11-12000 B.P. Preliminary pollen spectra show a relatively constant pattern with a dominance of grass pollen even during the middle Holocene.
Im SW Burkina Fasos (sechs Monate Regenzeit und durchschnittlich über 1000 mm Niederschlag) wurden mehrere Trockenwälder auf ihr Artenspektrum und die Bodenverhältnisse hin untersucht. Die Waldformationen fallen durch die Dichte der Gehölzbedeckung, ihren Lianenreichtum und das fast vollständige Fehlen von Gräsern auf. Typische Gehölzarten sind Anogeissus leiocarpus, Diospyros mespiliformis und die Liane Saba senegalensis. Der dichte Strauchunterwuchs und die fehlende Grasschicht verhindern das regelmäßige Eindringen von Buschfeuern. Wegen der Dichte und des Alters der Bäume belegen diese Waldformationen, daß an den Standorten, zumindest für einen sehr langen Zeitraum, kein Feldbau betrieben wurde. Daher konnten sich, auch auf eher als ungünstig zu bewertenden Böden, Trockenwälder ausbilden, die zumindest in ihrer Physiognomie der potentiellen natürlichen Vegetation entsprechen. Jedoch finden sich in den Wäldern oft Spuren menschlicher Aktivitäten aus der Vergangenheit, so z.B. Steinsetzungen, Siedlungshügel und Gruben. Außerdem lassen sich vielfach Anzeichen einer rezenten Nutzung beobachten, so z.B. für die Entnahme von Werkholz, das Schneiteln mancher Baumarten zur Viehfuttergewinnung, gelegentliche Beweidung und das Sammeln von Wildpflanzen.
Les ferrières sont par définition les amas des déchets de la réduction du fer. De par son origine elles constituent des lithosols qui ont beaucoup évolué dans l’espace et dans le temps. A notre connaissance très peu d’études se sont penchées sur cette végétation qui couvre actuellement les sites de réduction du fer. L’inventaire floristique de plusieurs sites en zone soudanienne montre la fréquence de certaines espèces sur les ferrières. L’étude de la chorologie de toutes les espèces confondues ligneuses et herbacées, montrent que la plupart sont constituées par des espèces zoochores et quelques espèces anémochores. Elles sont disséminées principalement par les animaux d’élevage, par les oiseaux. Cette communication synthétise les données des différentes prospections et les premiers résultats de nos observations et analyses. Elle a deux objectifs : de montrer l’importance des activités anthropiques dans la formation du paysage végétal d’une part, et d’autre part de mettre en évidence le processus de colonisation des sols nus et des ferrières en zone soudanienne.
Au Sahel du Burkina Faso, le diagramme pollinique d'Oursi fournit des évidences sur l'apparition de l'agriculture, il y a environ 3000 ans. A partir de ces faits, le but principal des recherches archéologiques dans le cadre du SFB 268 était de trouver et de fouiller des sites qui seraient à même d'apporter des informations sur cette période décisive autour de 3000 ans avant l'actuel. Pour cela, nous avons concentré notre travail sur les provinces du Séno et plus particulièrement de l'Oudalan. Le paysage de cette région est marqué par des dunes qui s'organisent grossièrement en cordons d'orientation nord-est/sud-ouest à travers notre terrain.
La variation dans l'utilisation des ressources végétales est liée aux changements de mode de vie. Le Burkina Faso fait parti des pays habituellement indiqués comme en voie de développement. Ce qualificatif est vrai si on ne regarde que la croissance technologique. Le pays accuse certes un retard sur ce plan, mais la population sait bel et bien développer son intelligence humaine pour faire face à telle ou telle situation. Ainsi, devant une mauvaise récolte, personne n'acceptera de mourir de faim tant que dans l'environnement naturel existeront tous les éléments nécessaires pour survivre: l'eau, les plantes et les animaux. A ce moment-là, le mode de vie change; il ne s'agit plus de récolter, mais il s'agit de prélever, de cueillir. La cueillette, c'était un mode de vie dans l'époque préhistorique. L'homme se rabat sur tout ce qui peut fournir un aliment substantiel: les gros tubercules, les feuilles les plus tendres, les fruits et les graines. Si les trois dernières catégories d'aliments ne posent pas trop de problèmes, la première et les autres organes souterrains sont en général toxiques. Et là encore, l'homme va développer son intelligence pour éliminer cette toxicité mais après une grande perte en vie humaine. Dans le but de savoir un peu plus sur ces différentes périodes de disette et de famine, nous avons mené une enquête à Ouahigouya (Yatenga) et à Toma (Sourou), deux zones qui appartenaient à un même cercle pendant l'époque coloniale, période de la suppression de la Haute-Volta. Par ailleurs nous voulons vérifier la marge d'erreur qu'on peut avoir lors d'une enquête ethnobotanique en se situant dans le temps et l'espace. Cette communication entre en plus dans le cadre de nos travaux de recherche sur l'histoire de la végétation et de l'utilisation des ressources végétales.
L'homme vivant de la cueillette existe toujours au Burkina Faso. Les espèces que nous allons exposer par la suite ne font pas l'objet d'une culture. La plupart certes sont des espèces protégées lors des défrichements. Elles caractérisent souvent les différents faciès de savane rencontrés à travers le pays. Certaines ont des usages généralisés en temps normal, d'autres le sont en temps de disette ou de soudure. Ces espèces ligneuses sont à usages culinaires par leurs feuilles, leurs graines et leurs exsudats. Leur composition chimique montre un certain équilibre énergétique à la consommation et permet de comprendre la santé de nos paysans malgré ce qu'on laisse entendre sur la pauvreté et la sous-alimentation. Dans le cadre de nos travaux pour une meilleure connaissance des espèces tant sur le plan taxonomique, biologique qu'ethnobotanique, nous avons mené depuis cinq ans une enquête sur les différentes utilisations des espèces ligneuses. Le présent travail concerne particulièrement les espèces ligneuses dont certains organes sont utilisés dans alimentation humaine. Nous nous sommes limités à ne parler que d'une vingtaine d'espèces.
La métallurgie du fer jouit d'un regain d'intérêt en Afrique depuis une décénnie. Alors que les diffusionistes et les antidiffusionistes se sont affrontés dans les années 1970, on assiste aujourd'hui à une nouvelle fièvre du "fer" où les chercheurs, mettant de côté l'idéologie, travaillent avec acharnement sur les fourneaux de réduction et sur toutes les traces de cette métallurgie. Les résultats obtenus sont déja impressionnants. L'environnement constituent aussi, désormais, une préoccupation majeure des chercheurs. Les recherches en paléométallurgie au Burkina Faso n'échappent pas totalemennt à cette critique. C'est pour attirer plus d'attention sur l'important complément sociologique des investigations archéologiques que nous proposons en ces lignes les quelques informations relatives aux conditions sociales des forgerons, potiers et potières, réunis dans plusieurs nationalités du Burkina Faso par une sorte de communauté de destin: les arts du feu.
Le Burkina Faso est situé dans la zone soudano-sahélienne où les cultures sont quelquefois aléatoires; dans ces conditions les plantes ligneuses occupent une place importante dans la vie socio-économique du pays. Pourtant, une sécheresses climatique persistante de ces dernières décennies a entraîné une mortalité massive de ces ligneux surtout dans la zone sahélienne. Cette forte dégradation des ressources naturelles est variable d’une zone géo-graphique à une autre pour des raisons diverses. Si les phénomènes généraux de cette dégradation de la végétation et leurs causes sont souvent décrits par de nombreux auteurs, il existe par contre très peu de connaissances détaillées et spécifiques en fonction des zones géographiques sur la menace qui pèse sur les différentes espèces. Dans l’absence de bases scientifiques fiables sur la végétation du passé pour chacune des régions qui permettrait ainsi d’établir avec précision la liste des espèces disparues, il est donc nécessaire de se baser sur la perception de la population rurale qui se trouve bien placée pour déceler tout changement dans la flore. Dans ce contexte, cette étude menée auprès des gourmantchés, vise surtout à identifier les espèces disparues ou celles en voie de disparition dans les différentes zones écologiques à l’est du Burkina Faso; en outre, elle aborde les raisons évoquées par ces populations pour expliquer cette menace qui pèse sur chacune des espèces. L’enquête a enfin contribué à connaître les solutions envisagées par ces dernières pour anéantir ou réduire la menace.
L’inventaire floristique du Burkina Faso est loin d’être clos. Les récentes investigations floristiques ont permis de recenser un grand nombre d’espèces qui n’avaient jamais été mentionnées sur la liste floristique nationale. Une partie de ces espèces sont d’ailleurs guinéocongolaises. Cet inventaire a concerné les aires classées et protégées situées dans le secteur Sudsoudanien. Les richesses floristiques se retrouvent concentrées dans ces aires classées et protégées car ce sont des formations qui jouissent d’une relative bonne gestion par rapport aux autres aires non protégées qui ont été fortement dégradées par l’homme. L’objectif de cette communication est de donner les informations issues de ces différentes investigations sur l’état de connaissance de la diversité végétale du Burkina Faso avec un accent particulier sur le mode de gestion et les utilisations de quelques espèces de la zone sud soudanienne.
Kagbeni and its irrigated oasis are surrounded by subdesert dwarf scrubland. In the present study, a list of 78 species of vascular plants is presented for Kagbeni and its immediate surroundings, supplemented with data on the distribution of the species within the entire Mustan District. The data are arrived from own investigations and the geobotanical literature. A phytogeographical analysis shows the prevalence of western over eastern elements. Species with a wide distribution in Eurasia, which constitute one third of the total flora of Kagbeni, are of great importance as weeds on arable fields and in ruderal places within the irrigated oasis. Their occurrence is closely related to human activity. Presumably, most of these weeds have reached the area under study in connection with agriculture a long time ago. Weeds from the New World, although recorded in other villages of Mustan District, have not been found in Kagbeni. The weed vegetation of Kagbeni is documented by nine vegetation releves, and is compared to releves from Jomsom and Mzrpha. A floristic gradient from south to north that has been detected by earlier investigations throughout the whole district can be reproduced at the local scale. With regard to the weed flora, the effects of different crops are minimal, compared to effects of altitude and other factors related to altitude.
Changes in settlement pattern and culture - the process of down-hill migration in Tula, Bauchi State
(1996)
The process of down-hill migration of the Tula people started during the 1920s and has not yet finished. The resulting present situation might give information how far terraces play any role in the economy, ecology and ideology of the Tula. Approaching this question from a socio-agricultural point of view some facts which indicate the pertaining or overcoming of traditional structures will be presented. In the following the land tenure system, the adoption of innovations and the role of women in agriculture will be discussed comparatively for Tula Wange and Tula Baule on the plateau, Fantami, which is generated by down-hill dwellers of Tula Wange, with its more or less bad farming conditions on shallow sandy soils and Kaltin, where the down migrants of Tula Baule settle in a more fertile area. Tula Wange numbers around 2000 households, Baule 1000, Fantami about 200 and Kaltin 350 of which the sample survey includes 15% in the plateau sites and 25% in the plain settlements.
Notre communication porte sur le thème suivant: "Anthropisation du couvert végétal dans la province de Namentenga et ses conséquences socioéconomiques: cas de la région de Tougouri, en zone subsahélienne" (centre-nord du Burkina Faso). A travers cette étude de cas, nous voulons attirer l'attention sur les problèmes environnementaux du Burkina Faso. En effet, les déficits pluviométriques cumulés, depuis quelques décennies, sont à l'origine de la dégradation des écosystèmes. La surexploitation des terres entraîne également l'épuisement des sols et la diminution des ressources végétales. Un telle situation n'est pas sans conséquence sur les activités socioéconomiques des populations. Le plan de notre communication sera donc comme suit: 1. Présentation du degré-carré de Tougouri, sur le plan physique 2. Dynamique du couvert végétal sous l'action anthropique, et les conséquences socioéconomiques 3. Perspectives d'avenir
La coupure que l'on constate dans les forêts denses africaines au niveau du Togo et du Bénin soulève de nombreuses questions sur les rapports forêt/savane au cours des derniers millénaires. Le projet Dahomey Gap vise à y répondre, par une approche pluridisciplinaire intégrant botanique et histoire de la végétation dans le Sud-Bénin et le Sud-Ouest du Nigéria. A partir de travaux déjà avancés sur la végétation du Bénin et des premières prospections palynologiques, quelques aspects du projet sont exposés ici: tels la caractérisation des différentes formations forestières du Bénin, les premiers résultats sur l'histoire holocène de la végétation du Sud-Bénin (mangroves, forêts, savanes) enregistrée depuis près de 7000 ans dans les lagunes.
Population structure was estimated in a continuous population of a small land snail (Trochoidea geyeri). Mark-recapture experiments and randomly amplified polymorphic DNA analyses indicate that the population structure can be described by the isolation by distance model of Wright (1946). Estimates of density and dispersal suggest a neighbourhood size of 70-208 individuals on an area of 13-21 m². A principal component analysis of the randomly amplified polymorphic DNA data reveals clinal variation of genetic composition across the population, as predicted by the neighbourhood concept. An analysis of molecular variance indicates substantial genetic structuring. Comparisons of the genetic distances, expressed as euclidean distances among individuals, versus the geographic distance between sampling sites yield a highly significant positive correlation (Mantel test: r = 0.567, p<0.0001). The revealed pattern of populational subdivision on a microgeographic scale seems to be one of the principal processes generating and maintaining genetic diversity within populations of small land gastropods.
In the present study the population genetic structure of the terrestrial snail Pomatias elegans was related to habitat structure on a microspatial scale. The genetic variability of 1607 individuals from 51 sampling sites in five different populations in Provence, France, was studied with an allozyme marker using population genetic methods, Mantel tests and spatial autocorrelation techniques were applied to different connectivity networks accounting for the structural features of the landscape. It is suggested that the population structure is, to a large extent, a function of the habitat quality, quantified as population density, and of the spatial arrangement of the habitat in the landscape and not of the geographical distance per se. In fragmented habitats, random genetic drift was the prevailing force for sampling sites separated by a few hundred meters.
Background: Growth rate is central to the development of cells in all organisms. However, little is known about the impact of changing growth rates. We used continuous cultures to control growth rate and studied the transcriptional program of the model eukaryote Saccharomyces cerevisiae, with generation times varying between 2 and 35 hours.
Results: A total of 5930 transcripts were identified at the different growth rates studied. Consensus clustering of these revealed that half of all yeast genes are affected by the specific growth rate, and that the changes are similar to those found when cells are exposed to different types of stress (>80% overlap). Genes with decreased transcript levels in response to faster growth are largely of unknown function (>50%) whereas genes with increased transcript levels are involved in macromolecular biosynthesis such as those that encode ribosomal proteins. This group also covers most targets of the transcriptional activator RAP1, which is also known to be involved in replication. A positive correlation between the location of replication origins and the location of growth-regulated genes suggests a role for replication in growth rate regulation.
Conclusion: Our data show that the cellular growth rate has great influence on transcriptional regulation. This, in turn, implies that one should be cautious when comparing mutants with different growth rates. Our findings also indicate that much of the regulation is coordinated via the chromosomal location of the affected genes, which may be valuable information for the control of heterologous gene expression in metabolic engineering.
Length variations of repetitive sequences in different AT-rich loop-coding regions of mitochondrial 16S rDNA in two gastropod species were discovered during intraspecific haplotype surveys. Examination of the discrete length variation of the basic repeat unit in a phylogenetic framework led to the conclusion of a microsatellite-like mutational dynamic. The observations suggest that the presence of a repetitive sequence structure alone is sufficient to trigger this dynamic.
I analysed the importance of shell size, shell shape, habitat preferences and availability, experienced climate, active dispersal and influence of Pleistocene glaciations for the range sizes of 37 Western Palaearctic Helicidae s.l. species for which a phylogeny was available. In both cross-species and phylogenetically controlled analyses, the range sizes were positively correlated to climatic tolerance, shell size, active dispersal and influence of Pleistocene glaciations. In addition, range sizes increased significantly with latitude. Multiple regression suggested that, predominantly, the influence of Pleistocene glaciations, tolerance to large annual temperature ranges and shell size influenced the distributional range sizes. Habitat preference, range and availability, active dispersal and shell shape explained no additional variance. The results suggest that the processes influencing species range size of the Helicidae s.l. are mainly related to the climatic shifts after the Pleistocene.
Alzheimer's disease-related mutations in the presenilin-1 gene (PS1) are leading to an elevated production of neurotoxic beta-amyloid 1-42 and may additionally enhance oxidative stress. Here, we provide in vivo evidence indicating that brains of transgenic mice expressing different human Alzheimer-linked PS1 mutations exhibit a reduced activity of two antioxidant enzymes. For this purpose, mice transgenic for human PS1 and for single and multiple PS1 mutations were generated. Mice with multiple PS1 mutations showed a significantly decreased activity of the antioxidant enzymes Cu/Zn superoxide dismutase and glutathione reductase already at an age of 3-4 months. As expected, this effect was less pronounced for the mice with a single PS1 mutation. By contrast, animals bearing normal human PS1 showed significantly elevated enzyme activities relative to non-transgenic littermate controls.
Background Reliable taxonomic identification at the species level is the basis for many biological disciplines. In order to distinguish species, it is necessary that taxonomic characters allow for the separation of individuals into recognisable, homogeneous groups that differ from other such groups in a consistent way. We compared here the suitability and efficacy of traditionally used shell morphology and DNA-based methods to distinguish among species of the freshwater snail genus Radix (Basommatophora, Pulmonata). Results Morphometric analysis showed that shell shape was unsuitable to define homogeneous, recognisable entities, because the variation was continuous. On the other hand, the Molecularly defined Operational Taxonomic Units (MOTU), inferred from mitochondrial COI sequence variation, proved to be congruent with biological species, inferred from geographic distribution patterns, congruence with nuclear markers and crossing experiments. Moreover, it could be shown that the phenotypically plastic shell variation is mostly determined by the environmental conditions experienced. Conclusion Contrary to DNA-taxonomy, shell morphology was not suitable for delimiting and recognising species in Radix. As the situation encountered here seems to be widespread in invertebrates, we propose DNA-taxonomy as a reliable, comparable, and objective means for species identification in biological research.
Enhanced apoptosis and elevated levels of reactive oxygen species (ROS) play a major role in aging. In addition, several neurodegenerative diseases are associated with increased oxidative stress and apoptosis in neuronal tissue. Antioxidative treatment has neuro-protective effects. The aim of the present study was to evaluate changes of susceptibility to apoptotic cell death by oxidative stress in aging and its inhibition by the antioxidant Ginkgo biloba extract EGb761. We investigated basal and ROS-induced levels of apoptotic lymphocytes derived from the spleen in young (3 months) and old (24 months) mice. ROS were induced by 2-deoxy-D-ribose (dRib) that depletes the intracellular pool of reduced glutathione. Lymphocytes from aged mice accumulate apoptotic cells to a significantly higher extent under basal conditions compared to cells from young mice. Treatment with dRib enhanced this difference, implicating a higher sensitivity to ROS in aging. Apoptosis can be reduced in vitro by treatment with EGb761. In addition, mice were treated daily with 100mg/kg EGb761 per os over a period of two weeks. ROS-induced apoptosis was significantly reduced in the EGb761 group. Interestingly, this effect seemed to be more pronounced in old mice.
Apoptosis seems to be involved in immunosenescence associated with aging. Moreover, in lymphocytes (PBL) of patients with Alzheimer's disease, an increased susceptibility to the apoptotic pathway has been described possibly due to impaired protection of oxidative stress. Accordingly, it seemed to be of particular interest to investigate the contribution of normal aging to the susceptibility from human lymphocytes to programmed cell death. We could show that PBL from elderly individuals (>60 years) accumulate apoptosing cells to a significant higher extent in spontaneous and activation-induced cell death compared to younger controls (<35 years). Treatment with the oxidative stressor 2-deoxy-D-ribose or with agonistic-CD95-antibody pronounced this effect even more implicating a higher sensitivity to reactive oxygen species and a higher functional CD95 expression, respectively. In addition, expression of the activation markers HLA-DR and CD95 was significantly increased in CD3+-cells of aged subjects, while expression of CD25 did not seem to be affected by age. Expression of Bcl-2 was increased in aging and correlated with the number of apoptotic cells.
The relevance of physiological immune aging is of great interest with respect to determining disorders with pathologic immune function in aging individuals. In recent years, the relevance of changes in peripheral lymphocytes in age-associated neurologic diseases has become more evident. Due to the lack of immunological studies, covering more than one event after mitogenic activation, we envisaged a new concept in the present study, aiming to investigate several events, starting from T cell receptor (TCR) ligation up to T cell proliferation. In addition, we addressed the question whether changes are present in the subsets (CD4, CD8) with aging. Phosphorylation of tyrosine residues declines with increasing age in CD4+ cells. Fewer levels of CD69 positive cells after 4 h mitogenic activation, altered expression of cytokines (IL2, IFN-gamma and TNF-alpha; 22 h) and lower proliferation (72 h) were determined in aging. Moreover, it could be shown that CD8+ lymphocytes react more effectively to mitogenic stimulation with reference to CD69 expression and proliferation in both age groups (<35 and >60 years old). These data indicate that T cell activation, mediated by TCR engagement, is significantly impaired in aging and both subsets are affected. However, bypassing the TCR does not fully restore T cell function, indicating that there are more mechanisms involved than impaired signal transduction through TCR only. The results will be discussed in relation to their relevance in neurodegenerative and psychiatric disorders.
In vivo manipulation of interleukin-2 expression by a retroviral tetracycline (tet)-regulated system
(1999)
We have used the tetracycline (tet)-regulated system as described previously to evaluate the applicability of controlled gene expression in cancer gene therapy. As a model gene, we used the human interleukin-2 (IL-2) gene, which has been placed under the transcriptional control of the tetO/promoter. Human melanoma cells were transduced by two modified retroviral tet vectors containing the transactivator regulatory unit and the IL-2 gene driven by the tetO/promoter, respectively. In the absence of tet, IL-2 expression in the target cells was stable over several months. IL-2 production was in the range of 40 U/106 cells/24 hours. A fine tuning of IL-2 expression could be achieved by culturing the transduced cells with increasing doses of tet, whereby a concentration of 500 ng/mL tet in the culture medium abrogated IL-2 expression. Most importantly for clinical application, IL-2 expression by the transduced melanoma cells could also be regulated in vivo. When nu/nu mice were inoculated with the transduced tumor cells, they failed to develop tumors. Instead, the inhibition of IL-2 expression in the transduced tumor cells by oral administration of tet led to subcutaneous tumor growth; this growth rate was comparable with the growth rate of subcutaneously inoculated untransduced parental cells. The finding demonstrates the applicability of the tet-regulated system in cancer gene therapy.
Many cases of early-onset inherited Alzheimer's disease (AD) are caused by mutations in the presenilin-1 (PS1) gene. Expression of PS1 mutations in cell culture systems and in primary neurons from transgenic mice increases their vulnerability to cell death. Interestingly, enhanced vulnerability to cell death has also been demonstrated for peripheral lymphocytes from AD patients. We now report that lymphocytes from PS1 mutant transgenic mice show a similar hypersensitivity to cell death as do peripheral cells from AD patients and several cell culture systems expressing PS1 mutations. The cell death-enhancing action of mutant PS1 was associated with increased production of reactive oxygen species and altered calcium regulation, but not with changes of mitochondrial cytochrome c. Our study further emphasizes the pathogenic role of mutant PS1 and may provide the fundamental basis for new efforts to close the gap between studies using neuronal cell lines transfected with mutant PS1, neurons from transgenic animals, and peripheral cells from AD patients. Copyright 2001 Academic Press.
In large models of neuronal cell death, there is a tight correlation between Cdk5 deregulation and cell-cycle dysfunction. However, pathways that link Cdk5 to the cell cycle during neuronal death are still unclear. We have investigated the molecular events that precede p25/Cdk5-triggered neuronal death using a neuronal cell line that allows inducible p25 expression. In this system, no sign of apoptosis was seen before 24 hours of p25 induction. Thus, at that time, cell-cycle-regulatory proteins were analysed by immunoblotting and some of them showed a significant deregulation. Interestingly, after time-course experiments, the earliest feature correlated with p25 expression was the phosphorylation of the retinoblastoma protein (Rb). Indeed, this phosphorylation was observed 6 hours after p25 induction and was abolished in the presence of a Cdk5 inhibitor, roscovitine, which does not inhibit the usual Rb cyclin-D kinases Cdk4 and Cdk6. Furthermore, analyses of levels and subcellular localization of Cdk-related cyclins did not reveal any change following Cdk5 activation, arguing for a direct effect of Cdk5 activity on Rb protein. This latter result was clearly demonstrated by in vitro kinase assays showing that the p25-Cdk5 complex in our cell system phosphorylates Rb directly without the need for any intermediary kinase activity. Hence, Rb might be an appropriate candidate that connects Cdk5 to cell-cycle deregulation during neuronal cell death.
The identification of specific genetic (presenilin-1 [PS1] and amyloid precursor protein [APP] mutations) and environmental factors responsible for Alzheimer's disease (AD) has revealed evidence for a shared pathway of neuronal death. Moreover, AD-specific cell defects may be observed in many other nonneuronal cells (e.g., lymphocytes). Thus, lymphocytes may serve as a cellular system in which to study risk factors of sporadic, as well as genetic AD in vivo. The aim of our present study was to clarify whether lymphocytes bearing genetic or sporadic risk factors of AD share an increased susceptibility to cell death. Additionally we examined whether a cell typespecific vulnerability pattern was present and how normal aging, the main risk factor of sporadic AD, contributes to changes in susceptibility to cell death. Here, we report that lymphocytes affected by sporadic or genetic APP and PS1 AD risk factors share an increased vulnerability to cell death and exhibit a similar cell type-specific pattern, given that enhanced vulnerability was most strongly developed in the CD4+ T-cell subtype. In this paradigm, sporadic risk factors revealed the highest impact on cell type-specific sensitivity of CD4+ T cells to apoptosis. In contrast, normal aging results in an increased susceptibility to apoptosis of both, CD4+ and CD8+ T cells.
Introduction: Reactive oxygen species (ROS) have been implicated in neurodegeneration and seem to be involved in the physiology and pathophysiology of several diseases, including normal aging and Alzheimer’s disease (AD). Enhanced ROS production in aging or AD is not restricted to the brain, but can also been seen in several peripheral tissues. The objective of the present study was to evaluate whether the mechanisms involved in the generation of oxidative stress in normal senescence and Alzheimer’s disease are identical or not. Methods: We analysed intracellular basal levels of ROS in lymphocytes from AD patients and healthy young and aged not-demented subjects as well as ROS levels following stimulation with d-ribose and staurosporine in all three groups. ROS levels were measured by flow cytometry using the intracellular fluorescence dye dihydrorhodamine123 (DHR123). Results: Our study shows that AD lymphocytes have increased basal levels of ROS, low susceptibility to ROS stimulation by 2-deoxy-D-ribose (dRib) and an increased response to staurosporine when compared with age-matched controls. Discussion: The data suggest that the defect(s) responsible for enhanced ROS production in AD may involve different or additional biological pathways than those involved in enhanced ROS generation during aging.
As major sources of reactive oxygen species (ROS), mitochondrial structures are exposed to high concentrations of ROS and may therefore be particularly susceptible to oxidative damage. Mitochondrial damage could play a pivotal role in the cell death decision. A decrease in mitochondrial energy charge and redox state, loss of transmembrane potential (depolarization), mitochondrial respiratory chain impairment, and release of substances such as calcium and cytochrome c all contribute to apoptosis. These mitochondrial abnormalities may constitute a part of the spectrum of chronic oxidative stress in Alzheimer's disease. Accumulation of amyloid beta (Abeta) in form of senile plaques is also thought to play a central role in the pathogenesis of Alzheimer's disease mediated by oxidative stress. In addition, increasing evidence shows that Abeta generates free radicals in vitro, which mediate the toxicity of this peptide. In our study, PC12 cells were used to examine the protective features of EGb 761(definition see editorial) on mitochondria stressed with hydrogen peroxide and antimycin, an inhibitor of complex III. In addition, we investigated the efficacy of EGb 761 in Abeta-induced MTT reduction in PC12 cells. Moreover, we examined the effects of EGb 761 on ROS levels and ROS-induced apoptosis in lymphocytes from aged mice after in vivo administration. Here, we will report that EGb 761 was able to protect mitochondria from the attack of hydrogen peroxide, antimycin and Abeta. Furthermore, EGb 761 reduced ROS levels and ROS-induced apoptosis in lymphocytes from aged mice treated orally with EGb 761 for 2 weeks. Our data further emphasize neuroprotective properties of EGb 761, such as protection against Abeta-toxicity, and antiapoptotic properties, which are probably due to its preventive effects on mitochondria.
FGF-2, a potent multifunctional and neurotrophic growth factor, is widely expressed in the brain and upregulated in cerebral ischemia. Previous studies have shown that intraventricularly or systemically administered FGF-2 reduces the size of cerebral infarcts. Whether endogenous FGF-2 is beneficial for the outcome of cerebral ischemia has not been investigated. We have used mice with a null mutation of the fgf2 gene to explore the relevance of endogenous FGF-2 in brain ischemia. Focal cerebral ischemia was produced by occlusion of the middle cerebral artery (MCAO). We found a 75% increase in infarct volume in fgf2 knock-out mice versus wild type littermates (P < 0.05). This difference in the extent of ischemic damage was observed after 24 h, and correlated with decreased viability in fgf2 mutant mice following MCA occlusion. Increased infarct volume in fgf2 null mice was associated with a loss of induction in hippocampal BDNF and trkB mRNA expression. These findings indicate that signaling through trkB may contribute to ameliorating brain damage following ischemia and that bdnf and trkB may be target genes of FGF-2. Together, our data provide the first evidence that endogenous FGF-2 is important in coping with ischemic brain damage suggesting fgf2 as one crucial target gene for new therapeutic strategies in brain ischemia.
Background The reciprocal (9;22) translocation fuses the bcr (breakpoint cluster region) gene on chromosome 22 to the abl (Abelson-leukemia-virus) gene on chromosome 9. Depending on the breakpoint on chromosome 22 (the Philadelphia chromosome – Ph+) the derivative 9+ encodes either the p40(ABL/BCR) fusion transcript, detectable in about 65% patients suffering from chronic myeloid leukemia, or the p96(ABL/BCR) fusion transcript, detectable in 100% of Ph+ acute lymphatic leukemia patients. The ABL/BCRs are N-terminally truncated BCR mutants. The fact that BCR contains Rho-GEF and Rac-GAP functions strongly suggest an important role in cytoskeleton modeling by regulating the activity of Rho-like GTPases, such as Rho, Rac and cdc42. We, therefore, compared the function of the ABL/BCR proteins with that of wild-type BCR. Methods We investigated the effects of BCR and ABL/BCRs i.) on the activation status of Rho, Rac and cdc42 in GTPase-activation assays; ii.) on the actin cytoskeleton by direct immunofluorescence; and iii) on cell motility by studying migration into a three-dimensional stroma spheroid model, adhesion on an endothelial cell layer under shear stress in a flow chamber model, and chemotaxis and endothelial transmigration in a transwell model with an SDF-1α gradient. Results Here we show that both ABL/BCRs lost fundamental functional features of BCR regarding the regulation of small Rho-like GTPases with negative consequences on cell motility, in particular on the capacity to adhere to endothelial cells. Conclusion Our data presented here describe for the first time an analysis of the biological function of the reciprocal t(9;22) ABL/BCR fusion proteins in comparison to their physiological counterpart BCR.
The interaction of T cells and antigen-presenting cells is central to adaptive immunity and involves the formation of immunological synapses in many cases. The surface molecules of the cells form a characteristic spatial pattern whose formation mechanisms and function are largely unknown. We perform computer simulations of recent experiments on geometrically repatterned immunological synapses and explain the emerging structure as well as the formation dynamics. Only the combination of in vitro experiments and computer simulations has the potential to pinpoint the kind of interactions involved. The presented simulations make clear predictions for the structure of the immunological synapse and elucidate the role of a self-organizing attraction between complexes of T cell receptor and peptide–MHC molecule, versus a centrally directed motion of these complexes.
In dieser Arbeit sollen zwei Themenkomplexe, jeder für sich außerordentlich interessant und vielschichtig, betrachtet und verknüpft werden. Das direkte Einbinden von lebenden Tieren in die Lehre des Lebendigen ist nicht nur sinnvoll, sondern wichtig und wird auch von den Rahmenplänen Biologie empfohlen. Mit dem Einsatz von Tieren im Unterricht wird sich an verschiedenen Stellen beschäftigt (z.B. OGILVIE & STINSON 1995). Der Klasse Reptilia kommt dabei aber vergleichsweise wenig Beachtung zu. Voraussetzung für die Haltung von Tieren in der Schule, die in der Öffentlichkeit steht und eine beachtliche Vorbildsfunktion inne hat, ist unter anderem, dass eine „artgerechte“ Unterbringung und Pflege möglich ist. Was unter der Bezeichnung einer „artgerechten Tierhaltung“ verstanden wird, ist alles andere als eindeutig. Deshalb soll die Thematik mit Bezug auf die Reptilienhaltung in der Schule beleuchtet werden.
The conditionally-lethal pso4-1 mutant allele of the spliceosomal-associated PRP19 gene allowed us to study this gene’s influence on pre-mRNA processing, DNA repair and sporulation. Phenotypes related to intron-containing genes were correlated to temperature. Splicing reporter systems and RT–PCR showed splicing efficiency in pso4-1 to be inversely correlated to growth temperature. A single amino acid substitution, replacing leucine with serine, was identified within the N-terminal region of the pso4-1 allele and was shown to affect the interacting properties of Pso4-1p. Amongst 24 interacting clones isolated in a two-hybrid screening, seven could be identified as parts of the RAD2, RLF2 and DBR1 genes. RAD2 encodes an endonuclease indispensable for nucleotide excision repair (NER), RLF2 encodes the major subunit of the chromatin assembly factor I, whose deletion results in sensitivity to UVC radiation, while DBR1 encodes the lariat RNA splicing debranching enzyme, which degrades intron lariat structures during splicing. Characterization of mutagen-sensitive phenotypes of rad2{Delta}, rlf2{Delta} and pso4-1 single and double mutant strains showed enhanced sensitivity for the rad2{Delta} pso4-1 and rlf2{Delta} pso4-1 double mutants, suggesting a functional interference of these proteins in DNA repair processes in Saccharomyces cerevisiae.
Chemically modified bases are frequently used to stabilize nucleic acids, to study the driving forces for nucleic acid structure formation and to tune DNA and RNA hybridization conditions. In particular, fluorobenzene and fluorobenzimidazole base analogues can act as universal bases able to pair with any natural base and to stabilize RNA duplex formation. Although these base analogues are compatible with an A-form RNA geometry, little is known about the influence on the fine structure and conformational dynamics of RNA. In the present study, nano-second molecular dynamics (MD) simulations have been performed to characterize the dynamics of RNA duplexes containing a central 1'-deoxy-1'-(2,4-difluorophenyl)-ß-D-ribofuranose base pair or opposite to an adenine base. For comparison, RNA with a central uridine:adenine pair and a 1'-deoxy-1'-(phenyl)-ß-D-ribofuranose opposite to an adenine was also investigated. The MD simulations indicate a stable overall A-form geometry for the RNAs with base analogues. However, the presence of the base analogues caused a locally enhanced mobility of the central bases inducing mainly base pair shear and opening motions. No stable ‘base-paired’ geometry was found for the base analogue pair or the base analogue:adenine pairs, which explains in part the universal base character of these analogues. Instead, the conformational fluctuations of the base analogues lead to an enhanced accessibility of the bases in the major and minor grooves of the helix compared with a regular base pair.
The radiation-sensitive mutant pso4-1 of Saccharomyces cerevisiae shows a pleiotropic phenotype, including sensitivity to DNA cross-linking agents, nearly blocked sporulation and reduced mutability. We have cloned the putative yeast DNA repair gene PSO4 from a genomic library by complementation of the blocked UV-induced mutagenesis and of sporulation in diploids homozygous for pso4-1. Sequence analysis revealed that gene PSO4 consists of 1512 bp located upstream of UBI4 on chromosome XII and encodes a putative protein of 56.7 kDa. PSO4 is allelic to PRP19, a gene encoding a spliceosome-associated protein, but shares no significant homology with other yeast genes. Gene disruption with a destroyed reading frame of our PSO4 clone resulted in death of haploid cells, confirming the finding that PSO4/PRP19 is an essential gene. Thus, PSO4 is the third essential DNA repair gene found in the yeast S.cerevisiae.
Das Thema der vorliegenden Arbeit war die molekulargenetische Charakterisierung der Funktion der Glukosesensoren Snf3 und Rgt2 in der Hefe S. cerevisiae. Snf3 und Rgt2 gehören zur Familie der Hexosetransporter. Sie unterscheiden sich von ihnen jedoch in ihrer Funktion als Glukosesensoren wie auch durch ihre ungewöhnlich langen Cterminalen Domänen. Snf3 und Rgt2 sind integrale Membranproteine, die als Reaktion auf extrazelluläre Glukose Signale auslösen, die zur Expression bestimmter Hexosetransporter führt. Einige Komponenten, die an der Signaltranduktion beteiligt sind, wurden bereits identifiziert. Jedoch ist der genaue Mechanismus, der zur Expression der Hexostransporter führt, noch nicht vollständig aufgeklärt. Im ersten Teil dieser Arbeit wurden die Proteine Snf3, Rgt2, Mth1, Std1 und Rgt1 auf direkte Interaktionen untereinander getestet, um Einblicke in den molekularen Mechanismus der Signaltransduktion zu erhalten. Desweiteren sollte festgestellt werden, ob die Protein-Wechselwirkungen von der C-Quelle abhängig sind. Es konnte gezeigt werden, dass zwischen den Membranproteinen Rgt2 bzw. Snf3 und den löslichen Proteinen Mth1 bzw. Std1 Interaktionen in Abhängigkeit von Glukose stattfanden. Diese Ergebnisse unterstützen das von Moriya und Johnston aufgestellte, gegenwärtige Modell für eine glukoseinduzierte HXT Genexpression. Im zweiten Teil dieser Arbeit wurde geprüft, ob sich aus dem Glukosesensor Snf3 durch eine Aminosäuresubstitution ein bifunktionaler Sensor für Glukose und Galaktose erzeugen läßt. Dazu wurden die für den Galaktosetransport verantwortlichen Aminosäuren in den homologen Positionen von Snf3 ausgetauscht. Die Bestimmungen der Regulation des Snf3-kontrollierten HXT7 Promotors ergaben, dass das mutierte Snf3 Protein, wie das Wildtyp-Snf3 Protein, eine normale Glukosesensorfunktion ausübt aber keine Galaktosesensorfunktion vorzeigt.
Background: The flavin in its FMN and FAD forms is a versatile cofactor that is involved in catalysis of most disparate types of biological reactions. These include redox reactions such as dehydrogenations, activation of dioxygen, electron transfer, bioluminescence, blue light reception, photobiochemistry (as in photolyases), redox signaling etc. Recently, hitherto unrecognized types of biological reactions have been uncovered that do not involve redox shuffles, and might involve the reduced form of the flavin as a catalyst. The present work addresses properties of reduced flavin relevant in this context. Results: N(5)-H exchange reactions of the flavin reduced form and its pH dependence were studied using the 15N-NMR-signals of 15N-enriched, reduced flavin in the pH range from 5 to 12. The chemical shifts of the N(3) and N(5) resonances are not affected to a relevant extent in this pH range. This contrasts with the multiplicity of the N(5)-resonance, which strongly depends on pH. It is a doublet between pH 8.45 and 10.25 that coalesces into a singlet at lower and higher pH values. From the line width of the 15N(5) signal the pH-dependent rate of hydrogen exchange was deduced. The multiplicity of the 15N(5) signal and the proton exchange rates are little dependent on the buffer system used. Conclusion: The exchange rates allow an estimation of the pKa value of N(5)-H deprotonation in reduced flavin to be ≥ 20. This value imposes specific constraints for mechanisms of flavoprotein catalysis based on this process. On the other hand the pK ≈ 4 for N(5)-H protonation (to form N(5)+-H2) would be consistent with a role of N(5)-H as a base.