NEGATIVE CONTROL OF BACTERIAL-DNA REPLICATION BY A CELL-CYCLE REGULATORY PROTEIN THAT BINDS AT THE CHROMOSOME ORIGIN

Caulobacter crescentus divides asymmetrically generating two distinct cell types at each cell division: a stalked cell competent for DNA rep lication, and a swarmer cell that is unable to initiate DNA replicatio n until it differentiates into a stalked cell later in the cell cycle. The CtrA protein, a member of the response regulator family of the tw o-component signal transduction system, controls multiple cell cycle p rocesses in Caulobacter and is present in swarmer cells but absent fro m stalked cells. We report that CtrA binds five sites within the chrom osome replication origin in vitro. These sites overlap an essential Dn aA box and a promoter in the origin that is essential for replication initiation. Analysis of mutant alleles of ctrA and point mutations in one of the CtrA binding sites in the origin demonstrate that CtrA repr esses replication in vivo. CtrA-mediated repression at the origin thus restricts replication to the stalked cell type. Thus, the direct coup ling of chromosome replication with the cell cycle is mediated by the ubiquitous two-component signaling proteins.