The temporally regulated ctrA P1 promoter is critical for cellular development and morphology in Caulobacter crescentus

In the dimorphic aquatic bacterium Caulobacter crescentus, genes are transcribed immediately before their protein products are required. Groups of genes, or genetic modules, are temporally controlled by oscillating master regulators. Oscillation is driven by cell-cycle-dependent transcription and proteolysis. One of the master regulators is the transcription factor CtrA. ctrA has two temporally regulated promoters, P1 (weak) and P2 (strong), with P1 transcription occurring prior to P2 transcription. To investigate the role of the P1 promoter in cell cycle progression, we inactivated the ctrA P1 promoter. β-galactosidase transcriptional assays in rich PYE broth indicate a ~40% reduction in ctrA transcription that results in a ~40% reduction in CtrA protein accumulation in the ctrA P1 mutant compared to wild type C. crescentus. ctrA P1 mutants with a nonfunctional P1 promoter have severe growth defects and accumulate multiple chromosomes per cell. The cells elongate and some have ectopic poles, suggesting a polarity defect. Therefore, the ctrA P1 promoter is critical for the normal growth and development of C. crescentus.