AN ESSENTIAL PROTEASE INVOLVED IN BACTERIAL CELL-CYCLE CONTROL

Proteolytic inactivation of key regulatory proteins is essential in eu karyotic cell-cycle control. We have identified a protease in the euba cterium Caulobacter crescentus that is indispensable for viability and cell-cycle progression, indicating that proteolysis is also involved in controlling the bacterial cell cycle, Mutants of Caulobacter that l ack the ATP-dependent serine protease ClpXP are arrested in the cell c ycle before the initiation of chromosome replication and are blocked i n the cell division process. ClpXP is composed of two types of polypep tides, the ClpX ATPase and the ClpP peptidase, Site-directed mutagenes is of the catalytically active serine residue of ClpP confirmed that t he proteolytic activity of ClpXP is essential, Analysts of mutants lac king ClpX or ClpP revealed that both proteins are required in vivo for the cell-cycle-dependent degradation of the regulatory protein CtrA, CtrA is a member of the response regulator family of two-component sig nal transduction systems and controls multiple cell-cycle processes in Caulobacter, In particular, CtrA negatively controls DNA replication and our findings suggest that specific degradation of the CtrA protein by the ClpXP protease contributes to G(1)-to-S transition in this org anism.