Flagellar and chemotaxis gene expression in Caulobacter crescentus
Alexander, William Anthony
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Caulobacter crescentus builds surface structures at specific times in the cell cycle. One of these structures is a single flagellum, which is assembled at a defined cellular location. Chemotaxis proteins are also differentially synthesized and localized to a specific region of the cell. The 40 genes involved in flagella biogenesis (fla) and chemotaxis (che) are regulated in a trans-acting hierarchy. This study addresses the organization and regulation of both flagellar and chemotaxis genes in mutant and wild-type strains.;A specific fla gene, flgJ (encoding the 29K flagellin), was examined in many different genetic backgrounds in order to determine the effects of other fla gene mutations on the transcription and translation of flgJ. Flagellin synthesis was measured by an immunoprecipitation assay using antiflagellin antibodies. Nuclease S1 protection assays combined with flagellin and reporter gene immunoprecipitations proved that flgJ is transcriptionally regulated in these mutants.;Chemotaxis gene organization was studied by cloning, sequencing and characterizing a che gene cluster from C. crescentus. To do this a region of the chromosome containing a Tn5 insertion that inactivates methyltransferase activity (cheR) was cloned. Physical and biochemical analysis of eight Tn5 insertions in this region provided evidence that several che genes are organized in an operon. A bp region of the cloned operon was shown to have homology to the S. typhimurium Meche operon (tar-cheZ).