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dc.contributor.authorXu, Hong
dc.identifier.citationSource: Dissertation Abstracts International, Volume: 51-06, Section: B, page: 2757.;Advisors: Lucille Shapiro.
dc.description.abstractThe flagellum of C. crescentus is formed at a defined time in the cell cycle and at a specific position on the cell. It is composed of a transmembrane basal body, a hook and a helical filament. Genes encoding flagellar components are expressed temporally in an order that reflects the sequence of flagellar assembly. The ordered expression is controlled by a complex regulatory cascade.;To understand the mechanisms of transcriptional control, the promoter region of the hook operon was cloned and studied in detail. Deletion analysis revealed that a minimal promoter region ({dollar}-120{dollar} to {dollar}-8{dollar}) contains all the information necessary and sufficient for the temporal transcription, and partitioning of the hook operon transcript to the swarmer cells. A transcription fusion was constructed that retained the hook operon 5{dollar}\sp\prime{dollar} regulatory region but lacked any sequences from the transcribed region. The reporter gene fused to this regulatory region was correctly partitioned to the swarmer cell. Multiple cis-acting elements within this region ({dollar}ftr{dollar} and "{dollar}ntrC{dollar}" at {dollar}-{dollar}100, a 13 bp consensus sequence at {dollar}-{dollar}37, and the region in between), are essential for transcriptional activation. Specific DNA-protein interactions in the upstream region of the promoter were detected by in vitro gel mobility shift assays. A transcription factor that binds specifically to a double stranded oligonucleotide corresponding to the {dollar}-{dollar}100 region was found to be temporally controlled in the same cell cycle time frame as the expression of hook operon.;It was found that the expression of the fibG promoter (hook operon) is influenced by cellular nitrogen metabolism in E. coli. To reveal regulatory interactions among flagellar genes, the promoter activity of two flagellar genes, including the hook operon, was assayed in thirteen fla mutant backgrounds. A negative regulation was found and shown to be super-imposed on the positive transacting control in the flagellar hierarchy. Therefore, it appears that coordinate positive regulation contributes to the initiation of transcription of the hook operon at a specific time and modulation of the level of hook operon expression. Negative control, as a response to the completion of specific steps in the assembly process, may be a mechanism to turn off gene expression.;Initial characterization of the motC and flbO gene cluster was carried out and complementation analysis revealed the gene organization and boundaries of the motC and flbO gene. Characterization of the motC region showed that this very large locus (5.2 Kb) contains at least two transcribed regions. The two transcripts found in the motC region were shown to be temporally controlled.
dc.publisherProQuest Dissertations & Theses
dc.subjectMolecular biology.
dc.titleA study of regulation of Caulobacter flagellar genes

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