Cell cycle-dependent polar localization of an essential bacterial histidine kinase that controls DNA replication and cell division

The master CtrA response regulator functions in Caulobacter to repress repl ication initiation in different phases of the cell cycle. Here, we identify an essential histidine kinase, CckA, that is responsible for CtrA activati on by phosphorylation. Although CckA is present throughout the cell cycle, it moves to a cell pole in S phase, and upon cell division it disperses. Re moval of the membrane-spanning region of CckA results in loss of polar loca lization and cell death. We propose that polar CckA functions to activate C trA just after the initiation of DNA replication, thereby preventing premat ure reinitiations of chromosome replication. Thus, dynamic changes in cellu lar location of critical signal proteins provide a novel mechanism for the control of the prokaryote cell cycle.