1,720,969 research outputs found
Biochemische Charakterisierung des Transkriptionsrepressors CopR und Evolution des CopR-Operators
Full text linkBakterien leben in Umgebungen sich ständig ändernder Bedingungen. Um sich an wechselnde Umweltverhältnisse anpassen zu können, wurde eine Vielzahl von Regulationsmechanismen entwickelt. Diese führen meist zur Aktivierung und/ oder Repression von Genen. Dabei wird die prokaryotische Genexpression durch die Regulation der Transkriptionsinitiation entscheidend beeinflußt. Die Initiation der Transkription bei Prokaryoten wird durch eine Vielzahl von Protein-Protein- und Protein-DNA-Interaktionen zwischen der RNA-Polymerase, der Promotor-DNA und Aktivator- und Repressor- Proteinen reguliert (Hochschild & Dove, 1998). Das E. coli-Genom enthält mehr als 300 Gene, die Proteine kodieren, die durch die Bindung an Promotoren die Transkription regulieren (Perez-Rueda & Collado-Vides, 2000). Die meisten dieser Proteine sind sequenzspezifische DNA-Bindungsproteine. Einige von ihnen regulieren die Transkription vieler Gene, wohingegen andere lediglich ein oder zwei Gene kontrollieren. Sieben Transkriptionsfaktoren (CRP, FNR, IHF, Fis, ArcA, NarL und Lrp) regulieren die Transkription von 50 % aller Gene in E. coli (Martinez-Antonio & Collado-Vides 2003). Auf der Basis von Sequenzanalysen können bakterielle Transkriptionsfaktoren unterschiedlichen Familien zugeordnet werden. Am besten charakterisiert sind die LacI-, AraC-, LysR-, CRP- und OmpR-Transkriptionsregulatoren. Die Strukturen vieler dieser Proteinesind bereits aufgeklärt worden (Huffman & Brennan, 2002)
In vitro-Charakterisierung regulatorischer und sensorischer RNAs in Prokaryoten
Full text linkIm Rahmen dieser Arbeit wurden eine cis-kodierte und eine trans-kodierte Antisense-RNA aus Bacillus subtilis sowie eine RNA-Thermometerstruktur aus Salmonella enterica in vitro strukturell und funktionell charakterisiert. In vitro-Analysen zur inhibitorischen Wirkung der cis-kodierten Antisense-RNA RNAIII haben gezeigt, dass die Ausbildung einer vollständigen Duplex mit ihrer Target-RNA (RNAII) nicht erforderlich ist. Ein Bindungsintermediat, das lediglich die simultane Beteiligung der Stem-Loops L3 und L4 von RNAIII erfordert, reicht als inhibitorischer Komplex für die Regulation der Replikation des Streptokokkenplasmides pIP501 aus. SR1 aus Bacillus subtilis ist eine 205 nt lange trans-kodierte Antisense-RNA, die durch direkte Basenpaarung regulierend auf ihr Target, ahrC-mRNA, einwirken kann. SR1 induziert strukturelle Veränderungen stromabwärts der Ribosomenbindungsstelle von ahrC-mRNA, wodurch die Translationsinitiation von AhrC verhindert wird. Die Translationskontrolle des agsA-Transkriptes in Salmonella enterica erfolgt über eine RNA-Thermometer-Struktur, die keinem der bisher identifizierten RNA-Thermometertypen entspricht
Cellular interactions in singles- and mixed-species biofilms of bacillus subtilis
Full text linkMicrobiology has had a profound impact on human societies and interests. It has provided solutions for diseases and changed entire industries. In nature, microorganisms commonly live in sessile communities called biofilms. These communities have high cell densities that promote the development of communications networks based on signaling molecules, and also allow for complex interactions to form among cells forming part of the biofilm. Furthermore, cells living in natural environments are often exposed to members of other species, which may become collaborative partners, or compete for resources. The recent development of better molecular biology tools and more sophisticated microscopy techniques, along with the application of social theory and big-data informatic approaches to the study of large microbial populations has brought forward the novel field of sociomicrobiology, which tries to better understand how microbes interact with one another. This dissertation presents a comprehensive review of the current knowledge of the development of biofilms by the Gram-positive model bacterium Bacillus subtilis, with a focus on the mechanisms and signals that mediate the interactions that this bacterium can establish, both among its own cells and with those of other species. It includes original research on the interactions that B. subtilis can develop with other soil bacteria, both as active members of a predator-prey relationship, and as providers of environmental cues that change the structure of B. subtilis biofilms. Additionally, the present work includes investigations on the genetic differences between B. subtilis strains and strain variants that impact phenotypic social behavior and biofilm formation. This dissertation also includes the first comprehensive inquiry about the total effect that a family of regulatory phosphatases has upon the population heterogeneity of B. subtilis and its adaptability to diverse environments and growth conditions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Two dual-function regulatory sRNAs in Bacillus subtilis, and their role in RNA degradation and sporulation
Full text linkThis study was conducted to identify a new function of the trans-encoded sRNA SR1 and to characterize a small protein encoded by the new potential dual-function sRNA SR7 in the Gram-positive model organism B. subtilis. The small RNA SR1 was found to inhibit translation of kinA mRNA. Neither the SR1 encoded peptide SR1P plays any role in the regulation of kinA nor SR1 influences the stability of kinA mRNA. The role of SR1 in sporulation was confirmed by analysing its effects on the promoters of downstream genes controlled by KinA through Spo0A. No role of Hfq or CsrA in sporulation was observed. SR1 was found to decelerate sporulation when glucose is exhausted. Moreover, SR1 impacted spore properties. Spores formed in the absence of SR1 exhibited lower resistance to stress conditions and displayed an altered composition of spore coat proteins. The sr7 gene was tagged in its native locus with a C-terminal 3x FLAG tag and the synthesis of the small protein SR7P confirmed in Western blots. Threefold increased amounts of SR7P were produced under different stress conditions. In co-elution experiments the glycolytic enzyme enolase was identified as interaction partner for SR7P. The binding of SR7P to enolase in turn improved the binding of enolase to RNase Y present in the DLN of B. subtilis. By contrast, it had no effect on the interaction of enolase with PfkA also present in the DLN. Enolase carries ten times more RNase Y in the presence of SR7P. RNA is not bridging the interaction between SR7P and enolase. SR7P does not directly bind RNase Y. In vitro RNase Y activity assays revealed a role of SR7P in modulation of the activity of Eno-bound RNase Y. The role of SR7P in modulation of the activity of Eno-bound RNase Y was confirmed in vivo for rpsO mRNA. Taken together, both small RNAs SR1 and SR7 are involved in the regulation of sporulation and modulation of DLN in B. subtilis under glucose limiting and stress conditions
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Charakterisierung des Transkriptionsfaktors CcpN aus Bacillus subtilis
Full text linkKatabolitrepression, die Fähigkeit, nicht benötigte alternative Stoffwechselwege beim Vorhandensein einer bevorzugten Nahrungsquelle abzuschalten, ist eine wichtige Eigenschaft zahlreicher Bakterien. In Bacillus subtilis wird diese Aufgabe unter anderem vom Transkriptionsfaktor CcpN übernommen, welcher für die Transkription der Gene gapB, pckA und sr1 reprimieren kann. Im Rahmen dieser Arbeit wurde der erst vor kurzem identifizierte Transkriptionsfaktor detailliert untersucht. Es konnte gezeigt werden, dass CcpN an den drei oben genannten Promotoren jeweils 2 Operatoren besetzt und diese kooperativ bindet. Außerdem wurden mit Hilfe von in vitro-Transkriptions-Versuchen und CD-Spektroskopie ATP und saurer pH-Wert als Aktivatoren und ADP als Repressor der CcpN-Aktivität identifiziert. Weiterhin konnte der molekulare Mechanismus der Repression durch CcpN an den drei oben genannten Promotoren aufgeklärt werden. Dabei wurde gezeigt, dass CcpN an allen Promotoren gemeinsam mit der RNA-Polymerase binden kann und auch die Bildung eines offenen Komplexes erlaubt. Am gapB-Promotor inhibiert CcpN schließlich die Transkriptionsinitiation, während es am pckA- und sr1-Promotor die RNA-Polymerase durch Kontaktierung der α-Untereinheit am Promotor arretiert. Letztendlich wurde thyB als neues, bisher unbekanntes Ziel von CcpN identifiziert und gezeigt, dass CcpN dort als Aktivator wirken kann. Zusammenfassend wurde die Wirkungsweise von CcpN anhand eines ausführlichen Modells dargestellt und damit ein wichtiger Beitrag zum Verständnis der Katabolitrepression in Bacillus subtilis geleistet
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Topoisomerase IV can functionally replace all type 1A topoisomerases in Bacillus subtilis
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