570 Biowissenschaften; Biologie
Refine
Year of publication
Document Type
- Article (2093)
- Doctoral Thesis (737)
- Preprint (219)
- Part of Periodical (78)
- Book (16)
- Conference Proceeding (12)
- Part of a Book (10)
- Periodical (3)
- Report (2)
- Working Paper (2)
Language
- English (3174) (remove)
Is part of the Bibliography
- no (3174)
Keywords
- RNA (20)
- aging (20)
- SARS-CoV-2 (19)
- inflammation (18)
- taxonomy (17)
- Biochemistry (16)
- Podospora anserina (16)
- mitochondria (16)
- Cell biology (15)
- NMR (15)
Institute
- Biowissenschaften (1220)
- Biochemie und Chemie (550)
- Medizin (454)
- Biochemie, Chemie und Pharmazie (346)
- Institut für Ökologie, Evolution und Diversität (176)
- Senckenbergische Naturforschende Gesellschaft (160)
- Biodiversität und Klima Forschungszentrum (BiK-F) (123)
- Exzellenzcluster Makromolekulare Komplexe (116)
- MPI für Biophysik (104)
- Frankfurt Institute for Advanced Studies (FIAS) (94)
- Buchmann Institut für Molekulare Lebenswissenschaften (BMLS) (90)
- Physik (89)
- Zentrum für Biomolekulare Magnetische Resonanz (BMRZ) (83)
- Pharmazie (63)
- Sonderforschungsbereiche / Forschungskollegs (37)
- Informatik (36)
- MPI für Hirnforschung (35)
- Georg-Speyer-Haus (31)
- Geowissenschaften (25)
- Zentrum für Arzneimittelforschung, Entwicklung und Sicherheit (ZAFES) (25)
- Extern (21)
- Center for Membrane Proteomics (CMP) (12)
- Ernst Strüngmann Institut (11)
- Geowissenschaften / Geographie (11)
- Institut für sozial-ökologische Forschung (ISOE) (8)
- Geographie (7)
- LOEWE-Schwerpunkt für Integrative Pilzforschung (7)
- Universitätsbibliothek (5)
- Zentrum für Interdisziplinäre Afrikaforschung (ZIAF) (5)
- Informatik und Mathematik (4)
- Mathematik (4)
- SFB 268 (4)
- MPI für empirische Ästhetik (3)
- Neuere Philologien (2)
- Rechtswissenschaft (2)
- Starker Start ins Studium: Qualitätspakt Lehre (2)
- Fachübergreifend (1)
- Fachübergreifende Einrichtungen (1)
- Gesellschaftswissenschaften (1)
- Interdisziplinäres Zentrum für Neurowissenschaften Frankfurt (IZNF) (1)
- Kulturwissenschaften (1)
MicroRNAs (miRNAs) are critical post-transcriptional regulators in many biological processes. They act by guiding RNA-induced silencing complexes to miRNA response elements (MREs) in target mRNAs, inducing translational inhibition and/or mRNA degradation. Functional MREs are expected to predominantly occur in the 3’ untranslated region and involve perfect base-pairing of the miRNA seed. Here, we generate a high-resolution map of miR-181a/b-1 (miR-181) MREs to define the targeting rules of miR-181 in developing murine T-cells. By combining a multi-omics approach with computational high-resolution analyses, we uncover novel miR-181 targets and demonstrate that miR-181 acts predominantly through RNA destabilization. Importantly, we discover an alternative seed match and identify a distinct set of targets with repeat elements in the coding sequence which are targeted by miR-181 and mediate translational inhibition. In conclusion, deep profiling of MREs in primary cells is critical to expand physiologically relevant targetomes and establish context-dependent miRNA targeting rules.
Key Points:
* Deep profiling identifies novel targets of miR-181 associated with global gene regulation.
* miR-181 MREs in repeat elements in the coding sequence act through translational inhibition.
* High-resolution analysis reveals an alternative seed match in functional MREs.
MicroRNAs (miRNAs) are critical post-transcriptional regulators in many biological processes. They act by guiding RNA-induced silencing complexes to miRNA response elements (MREs) in target mRNAs, inducing translational inhibition and/or mRNA degradation. Functional MREs are expected to predominantly occur in the 3' untranslated region and involve perfect base-pairing of the miRNA seed. Here, we generate a high-resolution map of miR-181a/b-1 (miR-181) MREs to define the targeting rules of miR-181 in developing murine T-cells. By combining a multi-omics approach with computational high-resolution analyses, we uncover novel miR-181 targets and demonstrate that miR-181 acts predominantly through RNA destabilization. Importantly, we discover an alternative seed match and identify a distinct set of targets with repeat elements in the coding sequence which are targeted by miR-181 and mediate translational inhibition. In conclusion, deep profiling of MREs in primary cells is critical to expand physiologically relevant targetomes and establish context-dependent miRNA targeting rules.
The haloarchaeon Haloferax volcanii contains nearly 2800 small non-coding RNAs (sRNAs). One intergenic sRNA, sRNA132, was chosen for a detailed characterization. A deletion mutant had a growth defect and thus underscored the importance of sRNA132. A microarray analysis identified the transcript of an operon for a phosphate-specific ABC transporter as a putative target of sRNA132. Both the sRNA132 and the operon transcript accumulated under low phosphate concentrations, indicating a positive regulatory role of sRNA132. A kinetic analysis revealed that sRNA132 is essential shortly after the onset of phosphate starvation, while other regulatory processes take over after several hours. Comparison of the transcriptomes of wild-type and the sRNA132 gene deletion mutant 30 min after the onset of phosphate starvation revealed that sRNA132 controls a regulon of about 40 genes. Remarkably, the regulon included a second operon for a phosphate-specific ABC transporter, which also depended on sRNA132 for rapid induction in the absence of phosphate. Competitive growth experiments of the wild-type and ABC transporter operon deletion mutants underscored the importance of both transporters for growth at low phosphate concentrations. Northern blot analyses of four additional members of the sRNA132 regulon verified that all four transcripts depended on sRNA132 for rapid regulation after the onset of phosphate starvation. Importantly, this is the first example for the transient importance of a sRNA for any archaeal and bacterial species. In addition, this study unraveled the first sRNA regulon for haloarchaea.
Autophagy is a highly conserved catabolic process cells use to maintain their homeostasis by degrading misfolded, damaged and excessive proteins, nonfunctional organelles, foreign pathogens and other cellular components. Hence, autophagy can be nonselective, where bulky portions of the cytoplasm are degraded upon stress, or a highly selective process, where preselected cellular components are degraded. To distinguish between different cellular components, autophagy employs selective autophagy receptors, which will link the cargo to the autophagy machinery, thereby sequestering it in the autophagosome for its subsequent degradation in the lysosome. Autophagy receptors undergo post-translational and structural modifications to fulfil their role in autophagy, or upon executing their role, for their own degradation. We highlight the four most prominent protein modifications – phosphorylation, ubiquitination, acetylation and oligomerisation – that are essential for autophagy receptor recruitment, function and turnover. Understanding the regulation of selective autophagy receptors will provide deeper insights into the pathway and open up potential therapeutic avenues.
Autophagy is a highly conserved catabolic process cells use to maintain their homeostasis by degrading misfolded, damaged and excessive proteins, nonfunctional organelles, foreign pathogens and other cellular components. Hence, autophagy can be nonselective, where bulky portions of the cytoplasm are degraded upon stress, or a highly selective process, where preselected cellular components are degraded. To distinguish between different cellular components, autophagy employs selective autophagy receptors, which will link the cargo to the autophagy machinery, thereby sequestering it in the autophagosome for its subsequent degradation in the lysosome. Autophagy receptors undergo post-translational and structural modifications to fulfil their role in autophagy, or upon executing their role, for their own degradation. We highlight the four most prominent protein modifications – phosphorylation, ubiquitination, acetylation and oligomerisation – that are essential for autophagy receptor recruitment, function and turnover. Understanding the regulation of selective autophagy receptors will provide deeper insights into the pathway and open up potential therapeutic avenues.
The use of phylogenies in ecology is increasingly common and has broadened our understanding of biological diversity. Ecological sub-disciplines, particularly conservation, community ecology and macroecology, all recognize the value of evolutionary relationships but the resulting development of phylogenetic approaches has led to a proliferation of phylogenetic diversity metrics. The use of many metrics across the sub-disciplines hampers potential meta-analyses, syntheses, and generalizations of existing results. Further, there is no guide for selecting the appropriate metric for a given question, and different metrics are frequently used to address similar questions. To improve the choice, application, and interpretation of phylo-diversity metrics, we organize existing metrics by expanding on a unifying framework for phylogenetic information.
Generally, questions about phylogenetic relationships within or between assemblages tend to ask three types of question: how much; how different; or how regular? We show that these questions reflect three dimensions of a phylogenetic tree: richness, divergence, and regularity. We classify 70 existing phylo-diversity metrics based on their mathematical form within these three dimensions and identify ‘anchor’ representatives: for α-diversity metrics these are PD (Faith's phylogenetic diversity), MPD (mean pairwise distance), and VPD (variation of pairwise distances). By analysing mathematical formulae and using simulations, we use this framework to identify metrics that mix dimensions, and we provide a guide to choosing and using the most appropriate metrics. We show that metric choice requires connecting the research question with the correct dimension of the framework and that there are logical approaches to selecting and interpreting metrics. The guide outlined herein will help researchers navigate the current jungle of indices.
Ferroptosis is an iron-dependent form of cell death, which is triggered by disturbed membrane integrity due to an overproduction of lipid peroxides. Induction of ferroptosis comprises several alterations, i.e. altered iron metabolism, response to oxidative stress, or lipid peroxide production. At the physiological level transcription, translation, and microRNAs add to the appearance and/or activity of building blocks that negatively or positively balance ferroptosis. Ferroptosis contributes to tissue damage in the case of, e.g., brain and heart injury but may be desirable to overcome chemotherapy resistance. For a more complete picture, it is crucial to also consider the cellular microenvironment, which during inflammation and in the tumor context is dominated by hypoxia. This graphical review visualizes basic mechanisms of ferroptosis, categorizes general inducers and inhibitors of ferroptosis, and puts a focus on microRNAs, iron homeostasis, and hypoxia as regulatory components.
Network graphs have become a popular tool to represent complex systems composed of many interacting subunits; especially in neuroscience, network graphs are increasingly used to represent and analyze functional interactions between multiple neural sources. Interactions are often reconstructed using pairwise bivariate analyses, overlooking the multivariate nature of interactions: it is neglected that investigating the effect of one source on a target necessitates to take all other sources as potential nuisance variables into account; also combinations of sources may act jointly on a given target. Bivariate analyses produce networks that may contain spurious interactions, which reduce the interpretability of the network and its graph metrics. A truly multivariate reconstruction, however, is computationally intractable because of the combinatorial explosion in the number of potential interactions. Thus, we have to resort to approximative methods to handle the intractability of multivariate interaction reconstruction, and thereby enable the use of networks in neuroscience. Here, we suggest such an approximative approach in the form of an algorithm that extends fast bivariate interaction reconstruction by identifying potentially spurious interactions post-hoc: the algorithm uses interaction delays reconstructed for directed bivariate interactions to tag potentially spurious edges on the basis of their timing signatures in the context of the surrounding network. Such tagged interactions may then be pruned, which produces a statistically conservative network approximation that is guaranteed to contain non-spurious interactions only. We describe the algorithm and present a reference implementation in MATLAB to test the algorithm’s performance on simulated networks as well as networks derived from magnetoencephalographic data. We discuss the algorithm in relation to other approximative multivariate methods and highlight suitable application scenarios. Our approach is a tractable and data-efficient way of reconstructing approximative networks of multivariate interactions. It is preferable if available data are limited or if fully multivariate approaches are computationally infeasible.
The membrane proximal external region (MPER) of the HIV-1 glycoprotein gp41 is targeted by the broadly neutralizing antibodies 2F5 and 4E10. To date, no immunization regimen in animals or humans has produced HIV-1 neutralizing MPER-specific antibodies. We immunized llamas with gp41-MPER proteoliposomes and selected a MPER-specific single chain antibody (VHH), 2H10, whose epitope overlaps with that of mAb 2F5. Bi-2H10, a bivalent form of 2H10, which displayed an approximately 20-fold increased affinity compared to the monovalent 2H10, neutralized various sensitive and resistant HIV-1 strains, as well as SHIV strains in TZM-bl cells. X-ray and NMR analyses combined with mutagenesis and modeling revealed that 2H10 recognizes its gp41 epitope in a helical conformation. Notably, tryptophan 100 at the tip of the long CDR3 is not required for gp41 interaction but essential for neutralization. Thus bi-2H10 is an anti-MPER antibody generated by immunization that requires hydrophobic CDR3 determinants in addition to epitope recognition for neutralization similar to the mode of neutralization employed by mAbs 2F5 and 4E10.
Poster presentation: Introduction We here address the problem of integrating information about multiple objects and their positions on the visual scene. A primate visual system has little difficulty in rapidly achieving integration, given only a few objects. Unfortunately, computer vision still has great difficultly achieving comparable performance. It has been hypothesized that temporal binding or temporal separation could serve as a crucial mechanism to deal with information about objects and their positions in parallel to each other. Elaborating on this idea, we propose a neurally plausible mechanism for reaching local decision-making for "what" and "where" information to the global multi-object recognition. ...
Aging of biological systems is controlled by various processes which have a potential impact on gene expression. Here we report a genome-wide transcriptome analysis of the fungal aging model Podospora anserina. Total RNA of three individuals of defined age were pooled and analyzed by SuperSAGE (serial analysis of gene expression). A bioinformatics analysis identified different molecular pathways to be affected during aging. While the abundance of transcripts linked to ribosomes and to the proteasome quality control system were found to decrease during aging, those associated with autophagy increase, suggesting that autophagy may act as a compensatory quality control pathway. Transcript profiles associated with the energy metabolism including mitochondrial functions were identified to fluctuate during aging. Comparison of wild-type transcripts, which are continuously down-regulated during aging, with those down-regulated in the long-lived, copper-uptake mutant grisea, validated the relevance of age-related changes in cellular copper metabolism. Overall, we (i) present a unique age-related data set of a longitudinal study of the experimental aging model P. anserina which represents a reference resource for future investigations in a variety of organisms, (ii) suggest autophagy to be a key quality control pathway that becomes active once other pathways fail, and (iii) present testable predictions for subsequent experimental investigations.
BACKGROUND: Acetogenic bacteria are able to use CO2 as terminal electron acceptor of an anaerobic respiration, thereby producing acetate with electrons coming from H2. Due to this feature, acetogens came into focus as platforms to produce biocommodities from waste gases such as H2+CO2 and/or CO. A prerequisite for metabolic engineering is a detailed understanding of the mechanisms of ATP synthesis and electron-transfer reactions to ensure redox homeostasis. Acetogenesis involves the reduction of CO2 to acetate via soluble enzymes and is coupled to energy conservation by a chemiosmotic mechanism. The membrane-bound module, acting as an ion pump, was of special interest for decades and recently, an Rnf complex was shown to couple electron flow from reduced ferredoxin to NAD+ with the export of Na+ in Acetobacterium woodii. However, not all acetogens have rnf genes in their genome. In order to gain further insights into energy conservation of non-Rnf-containing, thermophilic acetogens, we sequenced the genome of Thermoanaerobacter kivui.
RESULTS: The genome of Thermoanaerobacter kivui comprises 2.9 Mbp with a G+C content of 35% and 2,378 protein encoding orfs. Neither autotrophic growth nor acetate formation from H2+CO2 was dependent on Na+ and acetate formation was inhibited by a protonophore, indicating that H+ is used as coupling ion for primary bioenergetics. This is consistent with the finding that the c subunit of the F1FO ATP synthase does not have the conserved Na+ binding motif. A search for potential H+-translocating, membrane-bound protein complexes revealed genes potentially encoding two different proton-reducing, energy-conserving hydrogenases (Ech).
CONCLUSIONS: The thermophilic acetogen T. kivui does not use Na+ but H+ for chemiosmotic ATP synthesis. It does not contain cytochromes and the electrochemical proton gradient is most likely established by an energy-conserving hydrogenase (Ech). Its thermophilic nature and the efficient conversion of H2+CO2 make T. kivui an interesting acetogen to be used for the production of biocommodities in industrial micobiology. Furthermore, our experimental data as well as the increasing number of sequenced genomes of acetogenic bacteria supported the new classification of acetogens into two groups: Rnf- and Ech-containing acetogens.
LIN-2/7 (L27) domains are protein interaction modules that preferentially hetero-oligomerize, a property critical for their function in directing specific assembly of supramolecular signaling complexes at synapses and other polarized cell-cell junctions. We have solved the solution structure of the heterodimer composed of the L27 domains from LIN-2 and LIN-7. Comparison of this structure with other L27 domain structures has allowed us to formulate a general model for why most L27 domains form an obligate heterodimer complex. L27 domains can be divided in two types (A and B), with each heterodimer comprising an A/B pair. We have identified two keystone positions that play a central role in discrimination. The residues at these positions are energetically acceptable in the context of an A/B heterodimer, but would lead to packing defects or electrostatic repulsion in the context of A/A and B/B homodimers. As predicted by the model, mutations of keystone residues stabilize normally strongly disfavored homodimers. Thus, L27 domains are specifically optimized to avoid homodimeric interactions.
Species of the genus Blautia are typical inhabitants of the human gut and considered as beneficial gut microbes. However, their role in the gut microbiome and their metabolic features are poorly understood. Blautia schinkii was described as an acetogenic bacterium, characterized by a functional Wood–Ljungdahl pathway (WLP) of acetogenesis from H2 + CO2. Here we report that two relatives, Blautia luti and Blautia wexlerae do not grow on H2 + CO2. Inspection of the genome sequence revealed all genes of the WLP except genes encoding a formate dehydrogenase and an electron-bifurcating hydrogenase. Enzyme assays confirmed this prediction. Accordingly, resting cells neither converted H2 + CO2 nor H2 + HCOOH + CO2 to acetate. Carbon monoxide is an intermediate of the WLP and substrate for many acetogens. Blautia luti and B. wexlerae had an active CO dehydrogenase and resting cells performed acetogenesis from HCOOH + CO2 + CO, demonstrating a functional WLP. Bioinformatic analyses revealed that many Blautia strains as well as other gut acetogens lack formate dehydrogenases and hydrogenases. Thus, the use of formate instead of H2 + CO2 as an interspecies hydrogen and electron carrier seems to be more common in the gut microbiome.
The fungal interaction with plants is a 400 million years old phenomenon, which presumably assisted in the plants’ establishment on land. In a natural ecosystem, all plant-ranging from large trees to sea-grasses-are colonized by fungal endophytes, which can be detected inter- and intracellularly within the tissues of apparently healthy plants, without causing obvious negative effects on their host. These ubiquitous and diverse microorganisms are likely playing important roles in plant fitness and development. However, the knowledge on the ecological functions of fungal root endophytes is scarce. Among possible functions of endophytes, they are implicated in mutualisms with plants, which may increase plant resistance to biotic stressors like herbivores and pathogens, and/or to abiotic factors like soil salinity and drought. Also, endophytes are fascinating microorganisms in regard to their high potential to produce a great spectrum of secondary metabolites with expected ecological functions. However, evidences suggest that the interactions between host plants and endophytes are not static and endophytes express different symbiotic lifestyles ranging from mutualism to parasitism, which makes difficult to predict the ecological roles of these cryptic microorganisms. To reveal the ecological function of fungal root endophytes, this doctoral thesis aims at assessing fungal root endophytes interactions with different plants and their effects on plant fitness, based on their phylogeny, traits, and competition potential in settings encompassing different abiotic contexts. To understand the cryptic implication of nonmycorrhizal endophytes in ecosystem processes, we isolated a diverse spectrum of fungal endophytes from roots of several plant species growing in different natural contexts and tested their effects on different model plants under axenic laboratory conditions. Additionally,we aimed at investigating the effect of abiotic and biotic variables on the outcome of interactions between fungal root endophytes and plants.
In summary, the morphological and physiological traits of 128 fungal endophyte strains within ten fungal orders were studied and artificial experimental systems were used to reproduce their interactions with three plant species under laboratory conditions. Under defined axenic conditions, most endophytes behaved as weak parasites, but their performance varied across plant species and fungal taxa. The variation in the interactions was partly explained by convergent fungal traits that separate groups of endophytes with potentially different niche preferences. According to my findings, I predict that the functional complementarity of strains is essential in structuring natural root endophytic communities. Additionally, the responses of plant-endophyte interactions to different abiotic factors, namely nutrient availability, light intensity, and substrate’s pH, indicate that the outcome of plant-fungus relationships may be robust to changes in the abiotic environment. The assessment of the responses of plant endophyte interactions to biotic context, as combinations of selected dominant root fungal endophytes with different degrees of trait similarity and shared evolutionary history, indicates that frequently coexisting root-colonizing fungi may avoid competition in inter-specific interactions by occupying specific niches, and that their interactions likely define the structure of root-associated fungal communities and influence the microbiome impacts on plant fitness.
In conclusion, my findings suggest that dominant fungal lineages display different ecological preferences and complementary sets of functional traits, with different niche preferences within root tissues to avoid competition. Also, their diverse effects on plant fitness is likely host-isolate dependent and robust to changes in the abiotic environment when these encompass the tolerance range of either symbiont.
The extraordinary desiccation resistance of the opportunistic human pathogen Acinetobacter baumannii is a key to its survival and spread in medical care units. The accumulation of compatible solute such as glutamate, mannitol and trehalose contributes to the desiccation resistance. Here, we have used osmolarity as a tool to study the response of cells to low water activities and studied the role of a potential inorganic osmolyte, K+, in osmostress response. Growth of A. baumannii was K+-dependent and the K+-dependence increased with the osmolarity of the medium. After an osmotic upshock, cells accumulated K+ and K+ accumulation increased with the salinity of the medium. K+ uptake was reduced in the presence of glycine betaine. The intracellular pools of compatible solutes were dependent on the K+ concentration: mannitol and glutamate concentrations increased with increasing K+ concentrations whereas trehalose was highest at low K+. After osmotic upshock, cells first accumulated K+ followed by synthesis of glutamate; later, mannitol and trehalose synthesis started, accompanied with a decrease of intracellular K+ and glutamate. These experiments demonstrate K+ uptake as a first response to osmostress in A. baumannii and demonstrate a hierarchy in the time-dependent accumulation of K+ and different organic solutes.
A new artificial regulatory system for essential genes in yeast is described. It prevents translation of target mRNAs upon tetracycline (tc) binding to aptamers introduced into their 5'UTRs. Exploiting direct RNA–ligand interaction renders auxiliary protein factors unnecessary. Therefore, our approach is strain independent and not susceptible to interferences by heterologous expressed regulatory proteins. We use a simple PCR-based strategy, which allows easy tagging of any target gene and the level of gene expression can be adjusted due to various tc aptamer-regulated promoters. As proof of concept, five differently expressed genes were targeted, two of which could not be regulated previously. In all cases, adding tc completely prevented growth and, as shown for Nop14p, rapidly abolished de novo protein synthesis providing a powerful tool for conditional regulation of yeast gene expression.
As a centerpiece of antigen processing, the ATP-binding cassette transporter associated with antigen processing (TAP) became a main target for viral immune evasion. The herpesviral ICP47 inhibits TAP function, thereby suppressing an adaptive immune response. Here, we report on a thermostable ICP47-TAP complex, generated by fusion of different ICP47 fragments. These fusion complexes allowed us to determine the direction and positioning in the central cavity of TAP. ICP47-TAP fusion complexes are arrested in a stable conformation, as demonstrated by MHC I surface expression, melting temperature, and the mutual exclusion of herpesviral TAP inhibitors. We unveiled a conserved region next to the active domain of ICP47 as essential for the complete stabilization of the TAP complex. Binding of the active domain of ICP47 arrests TAP in an open inward facing conformation rendering the complex inaccessible for other viral factors. Based on our findings, we propose a dual interaction mechanism for ICP47. A per se destabilizing active domain inhibits the function of TAP, whereas a conserved C-terminal region additionally stabilizes the transporter. These new insights into the ICP47 inhibition mechanism can be applied for future structural analyses of the TAP complex.
RcsF, a proposed auxiliary regulator of the regulation of capsule synthesis (rcs) phosphorelay system, is a key element for understanding the RcsC-D-A/B signaling cascade, which is responsible for the regulation of more than 100 genes and is involved in cell division, motility, biofilm formation, and virulence. The RcsC-D-A/B system is one of the most complex bacterial signal transduction pathways, consisting of several membrane-bound and soluble proteins. RcsF is a lipoprotein attached to the outer membrane and plays an important role in activating the RcsC-d-A/B pathway. The exact mechanism of activation of the rcs phosphorelay by RcsF, however, remains unknown. We have analyzed the sequence of RcsF and identified three structural elements: 1) an N-terminal membrane-anchored helix (residues 3-13), 2) a loop (residues 14-48), and 3) a C-terminal folded domain (residues 49-134). We have determined the structure of this C-terminal domain and started to investigate its interaction with potential partners. Important features of its structure are two disulfide bridges between Cys-74 and Cys-118 and between Cys-109 and Cys-124. To evaluate the importance of this RcsF disulfide bridge network in vivo, we have examined the ability of the full-length protein and of specific Cys mutants to initiate the rcs signaling cascade. The results indicate that the Cys-74/Cys-118 and the Cys-109/Cys-124 residues correlate pairwise with the activity of RcsF. Interaction studies showed a weak interaction with an RNA hairpin. However, no interaction could be detected with reagents that are believed to activate the rcs phosphorelay, such as lysozyme, glucose, or Zn(2+) ions.
Polo-like kinase 1 (PLK1) is a crucial regulator of cell cycle progression. It is established that the activation of PLK1 depends on the coordinated action of Aurora-A and Bora. Nevertheless, very little is known about the spatiotemporal regulation of PLK1 during G2, specifically, the mechanisms that keep cytoplasmic PLK1 inactive until shortly before mitosis onset. Here, we describe PLK1 dimerization as a new mechanism that controls PLK1 activation. During the early G2 phase, Bora supports transient PLK1 dimerization, thus fine-tuning the timely regulated activation of PLK1 and modulating its nuclear entry. At late G2, the phosphorylation of T210 by Aurora-A triggers dimer dissociation and generates active PLK1 monomers that support entry into mitosis. Interfering with this critical PLK1 dimer/monomer switch prevents the association of PLK1 with importins, limiting its nuclear shuttling, and causes nuclear PLK1 mislocalization during the G2-M transition. Our results suggest a novel conformational space for the design of a new generation of PLK1 inhibitors.