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In dieser Arbeit wurde der chemische Ozonverlust in der arktischen Stratosphäre über elf Jahre hinweg, zwischen 1991 und 2002, mit Hilfe der so genannten "Ozon-Tracer Korrelationstechnik" (TRAC), untersucht. Bei dieser Methode werden Korrelationen zwischen Ozon und langlebigen Spurenstoffen im Verlauf des Winters im Polarwirbels beobachtet und so der jährliche akkumulierte Ozonverlust berechnet. Die Ergebnisse dieser Arbeit basieren im wesentlichen auf Messdaten der Satelliteninstrumente: HALOE (Halogen Occultation Experiment) auf UARS (Upper Atmosphere Research Satellite) und ILAS (Improved Limb Atmospheric Spectrometer) Instrument auf ADEOS (Advanced Earth Observing Satellite). Das HALOE Instrument misst seit Oktober 1991 kontinuierlich alle zwei bis drei Monate für einige Tage in höheren nördlichen Breiten. ILAS lieferte ausschließlich für den Winter 1996-97 Messungen, die über sieben Monate hinweg in hohen Breiten aufgenommen wurden. Aufgrund der eingeführten Erweiterungen und Verbesserungen der Methode in dieser Arbeit, konnte die Methode anhand einer detaillierten Studie für den Winter 1996-97 validiert werden. Die ILAS Messreihe wurde dazu verwendet, erstmals die Untersuchung der zeitlichen Entwicklung von Ozon-Tracer Korrelationen kontinuierlich für die gesamte Lebensdauer des Polarwirbels durchzuführen. Dabei wurden auch Korrelationen während der Bildung des Wirbels untersucht und im Besonderen mögliche Mischungsvorgänge zwischen Wirbelluft und Luftmassen außerhalb des Wirbels. Ausserdem wurde ein Vergleich der Ergebnisse von ILAS und HALOE Messdaten durchgeführt und Unterschiede in den Ergebnissen tiefgreifend analysiert. Basierend auf HALOE Messungen konnte die erweiterte TRAC Methode über elf Jahren hinweg angewendet werden. Damit war erstmals eine konsistente Analyse von Ozonverlust und Chloraktivierung über diesen Zeitraum möglich. Die Erweiterungen führten zu einer Verringerung und genauen Quantifizierung von Unsicherheiten der Ergebnisse. Ein deutlicher Zusammenhang zwischen meteorologischen Bedingungen, Chloraktivierung und dem chemischen Ozonverlust wurde deutlich. Weiterhin zeigte sich eine Abhängigkeit zwischen den meteorologischen Bedingungen und der Homogenität des Ozonverlustes innerhalb eines Winters, sowie der mögliche Einfluss von horizontaler Mischung auf Luftmassen in einem schwach ausgeprägten Polarwirbel. In dieser Arbeit wurde eine positive Korrelation zwischen den über die gesamte Lebensdauer des Wirbels auftretenden möglichen PSC-Flächen und den akkumulierten Ozonverlusten für die elf untersuchten Jahre deutlich. Es konnte darüber hinaus gezeigt werden, dass der Ozonverlust von deutlich mehr Einflüssen als nur von der Fläche möglichen PSC Auftretens bestimmt wird, sondern zum Beispiel von der Stärke der Sonneneinstrahlung abhängt. Außerdem lassen sich Auswirkungen von Vulkanausbrüchen, wie zum Beispiel im Jahr 1991 der des Mount Pinatubo, identifizieren.
Die Infrarotspektroskopie in Verbindung mit photoaktivierbaren Substraten wurde zur Untersuchung von Substrat-Protein-Wechselwirkungen eingesetzt. Dabei wurden Konformationsänderungen der Ca2+-ATPase des Sarkoplasmatischen Retikulums bei Bindung des Nukleotids, der Phosphorylierung der ATPase und der Hydrolyse des Phosphoenzyms beobachtet. Verwender wurden das native Substrat ATP und seine Analoga ADP, AMPPNP, 2'-deoxyATP, 3'-deoxyATP, ITP, AMP, Pyrophosphat, Ribosetriphosphat und TNP-AMP beobachtet. Diese Analoga waren an spezifischen funktionellen Gruppen des Substrats ATP modifiziert. Modifikation der 2'- und 3'-OH Gruppe des Ribosetriphosphats, der beta- und gamma-Phosphatgruppe und der Aminogruppe des Adenins reduzieren das Ausmaß an bindungsinduzierten Konformationsänderungen. Ein besonders starker Effekt wird für die 3'-OH Gruppe und die Aminogruppe des Adenins beobachtet. Dies zeigt die strukturelle Empfindlichkeit des Nukleotid-ATPase Komplexes auf einzelne Wechselwirkungen zwischen dem Nukleotid und der ATPase. Die Wechselwirkungen einer bestimmten Ligandengruppe mit der ATPase hängen von Wechselwirkungen anderer Ligandengruppen mit die ATPase ab. Die TNP-AMP Bindung verursacht teilweise gegenläufige und kleinere Konformationsänderungen verglichen mit ATP. Die Bindungweise von TNP-AMP ist unterschiedlich zu der von ATP, AMPPNP und anderen Tri- und Diphosphat Nucleotiden. Die Phosphorylierung der ATPase wurde mit ITP und 2'-deoxyATP beobachtet. Ca2E1P wurde in gleichem Ausmaß mit ITP und 2'-deoxyATP wie mit ATP akkumuliert, obwohl das Ausmaß der Konformationsänderungen bei Ca2E1P-Bildung geringer ist. Änderungen der 2'- und 3'-OH des Ribosetriphosphats und der Aminogruppe des Adenins beeinflussen die Reaktionsgeschwindigkeit der Phosphorylierung der ATPase. Es gibt keine direkte Verbindung zwischen dem Ausmaß der Konformationsänderung bei Nukleotid- Bindung und der Rate der Phosphorylierung. Das volle Ausmaß der ATP-induzierten Konformationsänderung ist nicht zwingend für die Phosphorylierung. Die Konformationen von Ca2E1N und Ca2E1P hängen vom Nukleotid ab. Dies weist darauf hin, dass die Struktur von ATPase Zuständen heterogener ist, als bisher erwartet. Die Aussagekraft und der Reichtum an Informationen in den Infrarotspektren zeigen, dass hiermit eine leistungsfähige Methode für die Untersuchung von Enzym-Substrat-Wechsel-Wirkungen und das räumliche Abtasten von Bindungstaschen zur Verfügung steht.
In this study we investigated the regulation of IL-18BPa by IFN-y in the context of colon cancer and human autoimmune diseases. IL-18BPa is a naturally occuring inhibitor that counteracts IL-18 bioactivity. By enhancing IFN-y production IL-18 has been introduced as pivotal mediator of TH1 immune responses. Indeed, many IL-18 effects are mediated by IFN-y. IL-18 bioactivity is connected with the pathogenesis of different inflammatory diseases, for instance, septic shock, colitis, Crohn's disease, myasthenia gravis, multiple sclerosis, rheumatoid arthritis, atherosclerosis, and organ transplant rejection. In addition, IL-18 has tumor-suppressive properties. IFN-y induced IL-18BPa expression was shown on protein and mRNA level in different colon carcinoma cell lines, organ cultures of colonic intestinal biopsy specimens, HaCaT keratinocytes as well as rheumatoid arthritis fibroblastlike synoviocytes (RA-FLS). The IFN-y-mediated induction of IL-18BPa appears to be a more general phenomenom. The capability of IFN-y to induce IL-18BPa also has been confirmed on the promoter level by performing luciferase reporter gene studies with two IL- 18BP promoter fragments. A GAS-site proximal to the transcription start site has been identified to be relevant for IFN-y-mediated induction of these two IL18BP promoter fragments. The induction of IL-18BPa is most likely mediated by STAT-1 in DLD-1 colon carcinoma cells. Sodium butyrate inhibited IFN-y-induced IL-18BPa expression in these cells. On the basis of our observations, we postulate a negative feedback mechanism, by which IFN-y-dependent and -independent IL-18 action might be counterregulated. In this model sodium butyrate is an additional player, that may interrupt the postulated negative feedback loop. A coculture system was performed to simulate an inflammatory TH1 response. This model which is more close to the in vivo situation, confirmed upregulation of IL-18BPa by endogenously produced IFN-y. The role of IL-18BPa is manifold and depends on IL-18 function in each particular case. In autoimmune diseases, for instance, which are often characterized by a TH1 polarized immune response, IL-18BPa might counterregulate IL-18 and/or IL-18-induced IFN-y bioactivity. Important examples are Crohn's disease and rheumatoid arthritis. In CD therapeutic use of IL-18BPa may therefore restore a hypothetically disturbed IL-18/IL-18BP balance. Concerning RA, IL-18BPa expression might contribute to protective functions of IFN-y, observed in different murine models for arthritis and in rheumatoid arthritis patients. Moreover, IL-18BPa might inhibit IL-18-mediated induction of subsequent cardinal inflammatory cytokines responsible for the pathogenesis of these diseases. Indeed, the pharmaceutical industry successfully used IL-18BP as therapeutic agent in a murine model of RA and in phase I clinical trials. On the contrary, in the context of carcinogenesis IFN-y- mediated IL-18BPa expression might be disadvantageous. By counterregulating the IL-18 arm of immune defenses against tumors, IL-18BP may have the potential to promote carcinogenesis. Our hypothesis is underlined by the observation that sodium butyrate, known to be protective in colon cancer, inhibited IFN-y-induced IL-18BPa expression. In parallel, IL-18-induced IFN-y is also responsible for iNOS induction. iNOS-derived NO provides a second possible way for inhibition of IFN-y-dependent and -independent tumor suppressive effects of IL-18. Finally, IFN-y-induced IL-18BPa expression was confirmed on the promoter level. This induction on the promoter level was associated with STAT-1 binding to the GAS element proximal to the start of transcription. It is tempting to speculate that blockage of the cytokine cascade upstream of IL-1 and TNF- a on the level of IL-18 may be of therapeutic benefit. Our data reflect the relationship between inflammation and cancer, in that inflammatory cells and cytokines found in tumors are likely to contribute to tumor growth, progression, and immunosuppression than they are to mount an effective host antitumour response.
In the recent years, high-resolution conditions have been established in solid-state NMR by the combination of magic angle spinning, state-of-the-art r.f. pulse schemes and the introduction of ultra-high magnetic fields. Similar to what is now routine in solution-state NMR, this has opened the way for structure determination by HR-SSNMR methods. Complete structural or dynamical characterization of the biomolecule of interest is most easily achieved if multiple or even uniformly [13C, 15N]-labeled versions are studied. In a first step, experiments that allow the complete assignment of the 13C and 15N resonances have been recently designed. To date, nearly complete chemical shift assignments were reported for two well-ordered proteins, the ±-spectrin SH3 domain and the Crh protein. The SSNMR analysis of the later protein has been presented in Section 4.1. For SSNMR applications, not the molecular size or solubility, but the spectral resolution can be of crucial importance. Experimental parameters and sample inherent conditions such molecular disorder may reduce the overall spectral dispersion. In these circumstances, techniques that allow for spectral simplification without the need of elaborated biochemical procedures (of isotopelabeling) are of special importance. In Section 2, several spectral editing methods have been proposed. These methods not only select resonances due to changesin the physical and chemical environment of the nucleus but they can also directly probe molecular properties such as dynamics and conformational heterogeneity. Once the chemical shifts are available for the biomolecule of interest, methods that permit to obtain structural restraints can be applied. In the case of multiply isotope labeled proteins, such techniques can in principle result in multiple structural parameters. In Section 3.1, we have shown that, similar to solution-state NMR, secondary chemical shifts can be readily employed to study the local backbone conformation. Inaddition, distance constraints between protons may be encoded in high-resolution on rare spins like 13C and 15N and measured. Finally, carbon-carbon constraints may be probed by employing frequency selective r.f. pulse schemes. These dihedral and distance constraints may subsequently lead to the determination of protein secondary to tertiary structure from a single protein sample. In Section 4.2,we have shown that high-affinity ligand binding to membrane proteins can be investigated with solid-state NMR. Here, the neuropeptide neurotensin which binds to the Gprotein coupled receptor NTS1 in sub-nanomolar affinity was investigated.Except for the case of rhodopsin, there is currently no information on the high-resolution structure of any other GPCR or a corresponding high-affinity ligand.Our SSNMR results identify, for the first time, a distinct binding mode of neurotensin that could be of considerable relevance for further pharmacological studies. As exemplified in section 4.3, HR-SSNMR based structural studies can also assist in refining existing (X-ray or solution-state NMR) membrane-protein structures. The presented results provide, for the first time, direct experimental evidence for a double occupancy of the Q0 binding site in the ubiquinone-bc1 complex and may provide the basis for the complete 3D structural determination of the ubiquinone binding pocket. Advancements regarding sample preparation (for example, including modular labeling, in vitro expression and intein technology) and improvements in NMR hardware instrumentation could open up new areas of solid-state NMR research such as the investigation of large protein-protein complexes or the complete 3D characterization of larger membrane proteins. Solid-state NMR studies of multiply-labeled biomolecules will furthermore profit from improved procedures for calculating 3D structures, in particular in the presence of ambiguousor a limited number of structural constraints. Unlike X-ray crystallography, protein motion does not hinder solid-state NMR methods. In fact, complementary to solution-state NMR, it may provide a very efficient means to study protein folding, flexibility and function under biologically relevant conditions. Hand in hand with solution-state techniques and crystallographic methods, solid-state NMR could provide insight into protein function and the chemistry of life with unprecedented accuracy and flexibility.
Im ersten Teil dieser Arbeit sind Protein-Protein Docking-Studien dokumentiert. Bis heute konnten die meisten Protein-Komplex-Strukturen nicht experimentell aufgeklärt werden, so auch die beiden oben genannten Elektrontransfer-Komplexe. Nach einem erfolgreichen Test wurden verschiedene Cytochrom c Oxidase:Cytochrom c Paare mit der gleichen Methode gedockt: COX aus Paracoccus denitrificans mit Pferdeherz Cytochrom c und COX mit dem löslichen Fragment des membrangebundenen Cytochrom C552 (beide aus P. denitrificans). Im zweiten Teil dieser Arbeit wurde die diffusive Annäherung des Cytochrom c an die Cytochrom c Qxidase mit der Brownschen Dynamik Methode simuliert. Die Diffusionsbewegung eines Brownschen Teilchens in wässriger Lösung wird durch die Langevin-Gleichung bestimmt. Der auf dieser Gleichung fußende Ermak-McCammon-Algorithmus ist Grundlage der Simulationsmethode. Die so ermittelten Raten für COX und Pferdeherz, sowie für COX und Cytochrom C552, wurden dann mit experimentell gewonnenen Raten verglichen. Da die Elektrostatik für den Annäherungsprozeß dieser Proteine eine so gewichtige Rolle spielt, wirken sich Mutationen, die mit einer Ladungsänderung einhergehen, merklich aus. Dies ist vor allem dann der Fall, wenn sich die Mutation in der Nähe der Bindungsstelle befindet. Aus dem gleichen Grund ist die Assoziationsrate auch stark von der Ionenstärke der umgebenden Lösung abhängig. Steigt die Ionenkonzentration wird die elektrostatische Komplementarität der Bindingsstellen der beiden Makromoleküle stärker abgeschirmt, und die Rate sinkt. Diese beiden relativen Trends konnten durch die Simulationen gut reproduziert und bestätigt werden. Allerdings liegen die absoluten Resultate merklich über den experimentell gemessenen Raten. Es ist sehr gut möglich, daß post-diffusive Effekte, die nicht in einer Brownschen Dynamik Simulation von starren Körpern berücksichtigt werden können, die Raten erniedrigen. Um den Einfluß der Membranumgebung auf die Wechselwirkung des Elektrontransportsystems zu untersuchen. wurde eine DPPC Doppelschicht um die Oxidase modelliert und energieminimiert. Mit Poisson-Boltzmann Rechnungen wurde das elektrostatische Potential dieses Nanosystems untersucht und mit dem der einzelnen Oxidase verglichen. Durch einen modifizierten Set-up konnten dann auch für dieses Membransystem Brownsche Dynamik Simulationen durchgeführt werden. Der Vergleich mit den vorhergehenden Simulationen ohne Membran erbrachte bemerkenswerte Ergebnisse. Während die Assoziationsraten für Pferdeherz Cytochrom c durch den Membraneinfluß erniedrigt wurden, stiegen sie im Fall des physiologischen Transferpartners c552. Pferdeherz Cytochrom c weist eine positive Nettoladung und einen ausgeprägten bipolaren Charakter auf. Eine große Zahl positiv geladener Seitenketten befindet sich auf der gleichen Hemisphäre wie die Bindungsstelle. Obwohl die DPPC Lipidmoleküle neutral sind, zeigten die Elektrostatikrechnungen, daß die Membranoberfläche abstoßend auf positive Ladungen wirkt. Da sich nun die Bindungsstelle der Oxidase für Cytochrom c nur etwa 10 Å oberhalb der Membran befindet, verringert sich die Wahrscheinlichkeit der Assoziation.
Mitogen activated protein kinases (MAPKs) are found in all eukaryotic cells and represent crucial elements in the signal transduction from the plasma membrane to the nucleus. Although a broad variety of extracellular stimuli activate MAPKs, they evoke very distinct cellular responses. The amplitude and duration of MAPK activation determine signal identity and ultimately cell fate. A tight and finely tuned regulation is therefore critical for a specific cellular response. The role and the regulation of extracellular signal-regulated kinase 5 (ERK5), a MAPK with a large and unique C-terminal tail, were studied in different cellular systems. The study highlights two aspects of ERK5 regulation: control of the phosphorylation state and regulated protein stability. In analogy to other MAPKs ERK5 is activated by dual phosphorylation of threonine and tyrosine residues in its activation motif. A first part of the study concentrates on whether and how the protein tyrosine phosphatase PTP-SL is involved in the downregulation of the ERK5 signal. The direct interaction of both proteins is shown to result in mutual modulation of their enzymatic activities. PTP-SL is a substrate of ERK5 and, independent of its phosphorylation, binding to the kinase enhances its catalytic phosphatase activity. On the other hand, interaction with PTP-SL does not only downregulate enzymatic ERK5 activity but also effectively impedes its translocation to the nucleus. The second part of this study focuses on the interaction of ERK5 with c-Abl and its oncogenic variants Bcr/Abl and v-Abl. In this study these tyrosine kinases are demonstrated to regulate ERK5 by two mechanisms: first, by induction of kinase activity and secondly, by stabilisation of the ERK5 protein. Stabilisation involves the direct interaction of unique ERK5 domains with Abl kinases and is independent of MAPK cascade activation. The level of ERK5 and its intrinsic basal activity – rather than its activation – are essential for v-Abl-induced transformation as well as for survival of Bcr/Abl-positive leukaemia cells. Stabilisation of ERK5 thus contributes to cell survival and should therefore be considered as an additional aspect in therapy of chronic myeloid leukaemia. Taken together, the results obtained in this study demonstrate that diverse pathways regulate ERK5 signalling by affecting kinase activity, localisation and protein stability. While the phosphatase PTP-SL is involved in negative regulation of ERK5, Abl kinases potently activate ERK5 and increase its half-life. Protein stabilisation thus is presented as a novel mechanism in the regulation of MAPKs.
Gegenstand dieser Arbeit sind Eigenschaften angeregter hadronischer Materie sowie physikalische Systeme, in denen diese Materie auftritt bzw. produziert wird. Die Beschreibung der stark wechselwirkenden Materie erfolgt in einem hadronischen, chiral-symmetrischen SU(3)L x SU(3)R Modell, welches die Saturierungseigenschaften von Kernmaterie und die Eigenschaften von Atomkernen reproduziert. Die Untersuchung heißer und dichter unendlicher hadronischor Materie zeigt, dass das vom Modell vorhergesagte Phasendiagramm stark von den Kopplungen der Baryonenresonanzen abhängt. Für kalte hadronische Materie ergibt die Einbeziehung des Baryonendekupletts und die Freiheit in deren Vektorkopplungen eine sehr große Bandbreite an verschiedenen Zustandsgleichungen. Für heiße hadronische Materie mit verschwindendem baryochemischen Potential zeigt sich ebenfalls eine starke Abhängigkeit der Eigenschaften hadronischer Materie von der Ankopplung der baryonischen Resonanzen. Es werden drei verschiedene Parametrisierungen betrachtet. Das resultierende Phasenübergangsverhalten variiert von einem "Crossover" über einen schwachen, zu einem doppelten Phasenübergang erster Ordnung. Es zeigt sich jedoch, dass die beobachteten Eigenschaften von Neutronensternen die Unbestimmtheit bzgl. der Vektorkopplung dieser Freiheitsgrade und damit der Zustandsgleichung deutlich verringern. Das Raum-Zeit Verhalten relativistischer Schwerionenkollisionen bei SPS- und RHIC-Energien wird mittels einer hydrodynamischen Simulation unter Benutzung der chiralen Zustandsgleichungen untersucht. Dabei spiegelt sich das unterschiedliche Phasenübergangsverhalten deutlich im Ausfrierverhalten der hadronischen Materie wider. Die im chiralen Modell berechneten Teilchenzahlverhältnisse werden mit den aus Schwerionenkollisionen von AGS- bis RHIC-Energien erhaltenen experimentellen Daten verglichen. Dabei zeigt sich, dass die verschiedenen Parametersätze des chiralen Modells und die Rechnungen für ein nichtwechselwirkendes, ideales Hadronengas eine ähnlich gute Beschreibung der gemessenen Weite liefern. Die deduzierten Ausfrierwerte für die Temperatur sind sensitiv auf das Phasenübergangsverhalten und liegen unterhalb der jeweiligen kritischen Temperatur. Die vorhergesagten Ausfriermassen sind in allen Parametrisierungen sehr ähnlich mit Abweichungen bis zu 15% von den entsprechenden Vakuumwerten. Die Untersuchung der Eigenschaften von Vektormesonen in dichter Materie erfolgt in der Mittleren-Feld- und in der HartreeNäherung. Hierbei zeigt sich eine signifikante Reduzierung der Teilchenmassen durch Vakuumpolarisationseffekte.
We consider the long-time behaviour of spatially extended random populations with locally dependent branching. We treat two classes of models: 1) Systems of continuous-time random walks on the d-dimensional grid with state dependent branching rate. While there are k particles at a given site, a branching event occurs there at rate s(k), and one of the particles is replaced by a random number of offspring (according to a fixed distribution with mean 1 and finite variance). 2) Discrete-time systems of branching random walks in random environment. Given a space-time i.i.d. field of random offspring distributions, all particles act independently, the offspring law of a given particle depending on its position and generation. The mean number of children per individual, averaged over the random environment, equals one The long-time behaviour is determined by the interplay of the motion and the branching mechanism: In the case of recurrent symmetrised individual motion, systems of the second type become locally extinct. We prove a comparison theorem for convex functionals of systems of type one which implies that these systems also become locally extinct in this case, provided that the branching rate function grows at least linearly. Furthermore, the analysis of a caricature model leads to the conjecture that local extinction prevails generically in this case. In the case of transient symmetrised individual motion the picture is more complex: Branching random walks with state dependent branching rate converge towards a non-trivial equilibrium, which preserves the initial intensity, whenever the branching rate function grows subquadratically. Systems of type 1) and systems of type 2) with quadratic branching rate function show very similar behaviour. They converge towards a non-trivial equilibrium if a conditional exponential moment of the collision time of two random walks of an order that reflects the variability in the branching mechanism is finite almost surely. The equilibrium population has finite variance of the local particle number if the corresponding unconditional exponential moment is finite. These results are proved by means of genealogical representations of the locally size-biased population. Furthermore, we compute the threshold values for existence of conditional exponential moments of the collision time of two random walks in terms of the entropy of the transition functions, using tools from large deviations theory. Our results prove in particular that - in contrast to the classical case of independent branching - there is a regime of equilibria with variance of the local number of particles.
One of the known apoptotic pathways in mammalian cells involves release of mitochondrial Cytochrome c into the cytosol. Cyt c then together with ATP or dATP induces a conformational change in the adaptator protein Apaf-1 (a homologue of the C. elegans CED4 protein) (Zou, Henzel et al. 1997), leading to its oligomerization and the recruitment of several pro-Casp-9 molecules. This protein complex assembly called "apoptosome" leads to the activation of Casp-9 which then initiates or amplifies the caspase cascade. The cell death program can be stalled at several points and we were interested in identifying new proteins inhibiting cell death downstream of Cyt c release. This thesis describes how I have screened a cDNA library derived from a pool of human breast carcinomas in a yeast-based survival screen, using the S. pombe yeast strain HC4 containing an inducible CED4 construct(James, Gschmeissner et al. 1997). The screen resulted in the identification of six proteins displaying cell death-inhibiting activity in S. pombe as well as anti-apoptotic potential in mammalian cells. Those six molecules were RoRet (Ruddy, Kronmal et al. 1997), Aven (Chau, Cheng et al. 2000), Fte-1/S3a (Kho, Wang et al. 1996), PGC2 (Padilla, Kaur et al. 2000; Goetze, Eilers et al. 2002), SAA1-2ß (Moriguchi, Terai et al. 2001) and FBP (Brockstedt, Rickers et al. 1998) of which I selected RoRet, Aven and Fte-1/S3a for further analysis. RoRet is a new anti-apoptotic molecule that can inhibit the mitochondrial pathway via its PRY-SPRY domain. RoRet does not seem to bind to Apaf-1, and does not co-localize with the activated Apaf-1/Caspase-9 complex. Aven was published to act as an anti-apoptotic protein and suggested to function via the recruitment of Bcl-XL to Apaf-1. This work shows that its C-terminal domain can bind to Apaf-1 and has a strong anti-apoptotic activity by itself. Moreover, Aven co-localizes with the activated Apaf-1/Caspase-9 complex suggesting that it is a component of the apoptosome. Furthermore, the expression of Aven is regulated in mammary glands during the pregnancy cycle. Fte-1/S3a has been already implicated in increased transformation capacity of v-Fos in fibroblasts (Kho and Zarbl 1992; Kho, Wang et al. 1996). This work shows that it has anti-apoptotic activity and can protect against Bak- and Apaf-1-induced apoptosis. It can bind directly to activated Apaf-1 at the linker domain between the WD40 repeats and the CED4-like domain, suggesting that it may protect by sequestering the activated Apaf-1 to some organelles whose nature remains to be determined. Moreover, expression studies on mRNA and protein level showed upregulation of Fte-1/S3a in colon, lung and kidney carcinoma. Hmgb1 (Flohr, Rogalla et al. 2001; Pasheva, Ugrinova et al. 2002; Stros, Ozaki et al. 2002) was identified during a survival screen performed with a NIH 3T3 mouse fibroblast cDNA library in a Bak-expressing yeast S. pombe strain. HMGB1 can protect against Bak-, UV-, FasL- and TRAIL-induced apoptosis. Significant overexpression of HMGB1 was found in breast and colon carcinoma, and elevated mRNA amounts were detected in uterus, colon and stomach carcinoma, suggesting that it may be a tumour marker (Brezniceanu et al., 2003).
Resistive Plate Chambers (RPCs) are gaseous parallel plate avalanche detectors that implement electrodes made from a material with a high volume resistivity between 10 high 7 and 10 high 12 omega cm. Large area RPCs with 2mm single gaps operated in avalanche mode provide above 98% efficiency and a time resolution of around 1 ns up to a flux of several kHz/cm high 2. These Trigger RPCs will, as an example, equip the muon detector system of the ATLAS experiment at CERN on an area of 3650 m high 2 and with 355.000 independent read out channels. Timing RPCs with a gas gap of 0.2 to 0.3mm are widely used in multi gap configurations and provide 99% efficiency and time resolution down to 50 ps. While their performance is comparable to existing scintillator-based Time-Of-Flight (TOF) technology, Timing RPCs feature a significantly, up to an order of magnitude, lower price per channel. They will for example equip the 176 m high 2 TOF barrel of the ALICE experiment at CERN with 160.000 independent read out cells. RPCs were originally operated in streamer mode providing large signals which simplifies readout electronics and gap uniformity requirements. However, high rate applications and detector aging issues made the operation in avalanche mode popular. This was also facilitated by the development of new highly quenching C2F4H2-based gas mixtures with small contents of SF6. While the physics of streamers is difficult to study, the avalanche mode opened the possibility for a detailed simulation of the detector physics processes in RPCs. Even though RPCs were introduced in the early eighties and have been (will be) used in experiments, there are still disagreements about the explanation of several aspects of the RPC performance. The high efficiency of single gap RPCs would require a large ionization density of the used gases, which according to some authors contradicts measurements. Even in the case of a large ionization density the gas gain has to be extremely large, in order to arrive at the observed RPC efficiency. This raises other questions: A very strong space charge effect is required to explain the observed small avalanche charges around 1 pC. Doubts have been raised whether an avalanche can progress under such extreme conditions without developing into a streamer. To overcome these difficulties, other processes, like the emission of an electron from the cathode, were suggested. Moreover, the shape of measured charge spectra of single gap RPCs differs largely from what is expected from the statistics of the primary ionization and the avalanche multiplication. In this thesis we discuss the detector physics processes of RPCs, from the primary ionization and the avalanche statistics to the signal induction and the read out electronics. We present Monte-Carlo simulation procedures that implement the described processes. While the fundament of the described model and some results were already published elsewhere [1], the subject of this thesis is the implementation of the space charge effect. We present analytic formulas for the electrostatic potential of a point charge in the gas gap of an RPC. These formulas were developed in collaboration with the University of Graz [2] and were published in [3, 4]. The simulation model presented in [1] is completed by the dynamic calculation of the space charge field using these formulas. Since the gas parameters like drift velocity and the Townsend and attachment coefficients depend on the electric field, they are calculated dynamically as well. The functional dependence of these parameters on the field is obtained with the simulation programs MAGBOLTZ and IMONTE. For the primary ionization parameters, we use the values that are predicted by the program HEED. While the described procedure only simulates the longitudinal avalanche development towards the anode of the RPC, we also present more dimensional models that allow a careful study of the transverse repulsive and attractive forces of the space charge fields, and of the consequences for the avalanche propagation. We shall show that the efficiencies of single gap Timing RPCs is indeed explained by the high primary ionization density (about 9.5 /cm as predicted by HEED) and a large effective Townsend coefficient (around 113 /mm as predicted by IMONTE). We show that the space charge field reaches the same magnitude as the applied electric field in avalanches at large gas gain. This strong space charge effect effectively suppresses large values for the avalanche charges. The shape of the simulated charge spectra is very similar to the measurements. Also the simulated average charges are close to the experimental results. RPCs are operated in a strong space charge regime over a large range of applied voltage, contrary to wire chambers. We apply only standard detector physics simulations to RPCs. The performance of Timing and Trigger RPCs is well reproduced by our simulations. The results concerning the space charge effect were presented and discussed at the 'RPC 2001' workshop [5] and on the '2002 NSS/MIC' conference [6].