A novel promoter motif for Caulobacter cell cycle-controlled DNA replication genes

Caulobacter crescentus contains a single chromosome that is replicated once during a defined period in the cell cycle. The onset of replication coincides with the stimulation of transcription of several genes involved in the replication process. Analysis of the C. crescentus homolog of dnaX, which in Escherichia coli encodes both the gamma and tau subunits of the DNA polymerase III holoenzyme, identified the dnaX transcription start site and showed that activity from the dnaX promoter is stimulated fourfold at the onset of DNA replication. We have identified a conserved sequence motif that is present in the promoter of dnaX and several other genes involved in the replication of DNA, all of which show an induction of transcription at the onset of chromosome replication. Independent mutations in the conserved sequence that lies between the -10 and -35 regions increased transcription, suggesting that a repressor may bind at this site. We propose that the coincident transcriptional activation of several dna genes at the swarmer to stalked cell transition occurs in response to cell cycle regulatory factors, in a manner analogous to the transient transcriptional regulation of flagellar and DNA methylation genes later in the cell cycle.