AN ESSENTIAL SINGLE-DOMAIN RESPONSE REGULATOR REQUIRED FOR NORMAL-CELL DIVISION AND DIFFERENTIATION IN CAULOBACTER-CRESCENTUS

Signal transduction pathways mediated by sensor histidine kinases and cognate response regulators control a variety of physiological process es in response to environmental conditions, Here we show that in Caulo bacter crescentus these systems also play essential roles in the regul ation of polar morphogenesis and cell division. Previous studies have implicated histidine kinase genes pleC and divJ in the regulation of t hese developmental events, We now report that divK encodes an essentia l, cell cycle-regulated homolog of the CheY/Spo0F subfamily and presen t evidence that this protein is a cognate response regulator of the hi stidine kinase PleC. The purified kinase domain of PleC, like that of DivJ, can serve as an efficient phosphodonor to DivK and as a phospho- DivK phosphatase, Based on these and earlier genetic results we propos e that PleC and DivK are members of a signal transduction pathway that couples motility and stalk formation to completion of a late cell div ision cycle event, Gene disruption experiments and the filamentous phe notype of the conditional divK341 mutant reveal that DivK also functio ns in an essential signal transduction pathway required for cell divis ion, apparently in response to another histidine kinase, We suggest th at phosphotransfer mediated by these two-component signal transduction systems may represent a general mechanism regulating cell differentia tion and cell division in response to successive cell cycle checkpoint s.