Conserved promoter motif is required for cell cycle timing of dnaX transcription in Caulobacter

Cells use highly regulated transcriptional networks to control temporally r egulated events. In the bacterium Caulobacter crescentus, many cellular pro cesses are temporally regulated with respect to the cell cycle, and the gen es required for these processes are expressed immediately before the produc ts are needed. Genes encoding factors required for DNA replication, includi ng dnaX, dnaA, dnaN, gyrB, and dnaK, are induced at the G(1)/S-phase transi tion. By analyzing mutations in the dnaX promoter, we identified a motif be tween the 10 and -35 regions that is required for proper timing of gene exp ression. This motif, named RRF (for repression of replication factors), is conserved in the promoters of other coordinately induced replication factor s. Because mutations in the RRF motif result in constitutive gene expressio n throughout the cell cycle, this sequence is likely to be the binding site for a cell cycle-regulated transcriptional repressor. Consistent with this hypothesis, Caulobacter extracts contain an activity that binds specifical ly to the RRF in vitro.