| As with all organisms, progression through the cell cycle in bacteria requires the precise coordination and timing of multiple cellular events. In the gram negative bacterium Caulobacter crescentus, this includes essential cell cycle processes such as DNA replication, chromosome segregation, and cell division, and includes morphological processes such as flagellar biogenesis and pili biogenesis. Prior work on the Caulobacter cell cycle has shown that regulated transcription plays a critical role in the timing and ordering of these processes. Here, I describe the use of nearly whole genome DNA microarrays for cataloging the wild type cell cycle expression profiles of 2966 Caulobacter genes. Analysis of these profiles led to the identification of 553 cell cycle-regulated transcripts. Examination of the known or predicted functions for these 553 genes led to three general conclusions: (i) genes are expressed immediately before or coincident with the time at which they are needed for function during the cell cycle, (ii) genes encoding proteins that function together as large molecular complexes are coexpressed, and (iii) biogenesis of large, multiprotein complexes is often temporally controlled by staged, hierarchical gene expression.; Included in this set of 553 cell cycle-regulated genes is a set of 40 known or predicted regulatory molecules. One of these regulatory genes encodes a response regulator, CtrA, which is essential for cell cycle progression. Combining microarray expression profiling of ctrA mutant strains with an immunoprecipitation-based genomic binding site analysis, I was able to identify 115 cell cycle genes that are directly controlled by CtrA. This CtrA regulon includes genes involved in nearly all aspects of polar morphogenesis as well as several essential cell cycle processes such as cell division, cell wall metabolism, DNA methylation, and cell cycle-regulated proteolysis. The results presented in this thesis have provided the outline for the complete genetic circuitry governing cell cycle progression in a bacterium. The new genes and pathways identified here as involved in Caulobacter 's regulatory network are now starting points for future, detailed dissections of the cell cycle. |
