Dokument: Identifizierung und Charakterisierung eines Transkriptionsregulators der Aconitase von Corynebacterium glutamicum
Titel: | Identifizierung und Charakterisierung eines Transkriptionsregulators der Aconitase von Corynebacterium glutamicum | |||||||
URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=3000 | |||||||
URN (NBN): | urn:nbn:de:hbz:061-20050104-001000-5 | |||||||
Kollektion: | Dissertationen | |||||||
Sprache: | Deutsch | |||||||
Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
Medientyp: | Text | |||||||
Autor: | Krug, Andreas [Autor] | |||||||
Dateien: |
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Beitragende: | Prof. Dr. Bott, Michael [Gutachter] Prof. Dr. Jaeger, Karl-Erich [Gutachter] | |||||||
Stichwörter: | Aconitase, AcnR, TetR, Tricarbonsäurezyklus, Transkriptionsregulator, Zitronensäurezyklusaconitase, AcnR, TetR, citric acid cycle, transcription regulator | |||||||
Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 570 Biowissenschaften; Biologie | |||||||
Beschreibungen: |
Zusammenfassung Ziel des ersten Teils dieser Arbeit war es, durch Transkriptom-Vergleiche von Valin- produzierenden Stämmen von Corynebacterium glutamicum mit dem Wildtyp potentielle neue Zielgene für die Verbesserung der Produzenten-Stämme zu finden. Ein Gen für ein putatives Transport-Protein, das bei dieser Analyse auffiel, wurde deletiert und überexprimiert, zeigte jedoch keinen Einfluss auf die Valin-Produktion. Im zweiten Teil der Arbeit wurden Untersuchungen zur Funktion und Regulation der Aconitase in C. glutamicum durchgeführt. Folgende Ergebnisse wurden dabei erzielt:
Abstract In the first part of this thesis the influence of valine production on global gene expression in Corynebacterium glutamicum was analysed in order to find new target genes for producer strain improvement. To this end, the transcriptomes of strain pairs differing in their valine production capability were compared using DNA microarrays covering the entire set of C. glutamicum genes. A putative transporter gene whose mRNA level was increased by valine production was deleted and overexpressed. However, valine synthesis was unaffected in the resulting strains. In the second part of this thesis the genetic regulation of the aconitase of C. glutamicum was analyzed. The activity of this enzyme was found to be 2.5- to 4-fold higher in propionate-, citrate- or acetate-grown cells than on glucose-grown cells. This variation was shown to be due to transcriptional regulation. A gene ( acnR ) encoding a TetR-type transcriptional regulator was found to be encoded immediately downstream of the aconitase gene ( acn ) in C. glutamicum . Deletion of acnR led to a 5-fold increase of the acn -mRNA level and of aconitase activity, suggesting that AcnR functions as repressor of acn . DNA microarray analyses indicated that acn is the primary target gene of AcnR in the C. glutamicum genome. Primer extension analyses revealed two transcriptional start sites of acn 110 and 113 bp upstream of the acn start codon. Purified AcnR was shown to be a homodimer which binds to the acn promoter in the region from -11 to -28 relative to the distal transcription start site. AcnR thus presumably acts by interfering with the binding of RNA polymerase. The acn - acnR organisation is conserved in all corynebacteria and mycobacteria with known genome sequence and a putative AcnR consensus binding motif (CAGNACnnncGTACTG) was identified in the corresponding acn upstream regions. Mutations within this motif inhibited AcnR binding. Since the activities of citrate synthase and isocitrate dehydrogenase were previously reported not to be increased during growth on acetate, our data indicate that aconitase is a major control point of TCA cycle activity in C. glutamicum and they identify AcnR as the first transcriptional regulator of a TCA cycle gene in the Corynebacterianeae . DNA affinity chromatography with the acn promoter region allowed the identification of a second transcriptional regulator of the acn gene, i.e. the RamA protein. RamA was enriched from C. glutamicum cells cultivated on acetate and probably functions as an activator of acn expression during growth on acetate. Except through AcnR and RamA, acn expression was also regulated by the iron content of the medium. Iron limitation led to decreased acn mRNA levels. Preliminary studies identified a transcriptional regulator of the AraC/XylS family which might be involved in the iron-dependent regulation of acn expression. Deletion of the acn gene resulted in a C. glutamicum strain that was glutamate-auxotrophic during growth on glucose minimal medium, confirming that there is only a single aconitase gene present in the C. glutamicum genome. | |||||||
Lizenz: | Urheberrechtsschutz | |||||||
Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Biologie | |||||||
Dokument erstellt am: | 04.01.2005 | |||||||
Dateien geändert am: | 12.02.2007 | |||||||
Promotionsantrag am: | 01.12.2004 | |||||||
Datum der Promotion: | 01.12.2004 |