IDENTIFICATION OF A NOVEL RESPONSE REGULATOR REQUIRED FOR THE SWARMER-TO-STALKED-CELL TRANSITION IN CAULOBACTER-CRESCENTUS

The onset of motility late in the Caulobacter crescentus cell cycle de pends on a signal transduction pathway mediated by the histidine kinas e PleC and response regulator DivK We now show that pleD, whose functi on is required for the subsequent loss of motility and stalk formation by the motile swarmer cell, encodes a 454-residue protein with tandem N-terminal response regulator domains D1 and D2 and a novel C-termina l GGDEF domain. The identification of pleD301, a semidominant suppress or of the pleC Mot phenotype, as a mutation predicted to result in a D -53-->G change in the D1 domain supports a role for phosphorylation in the PleD regulator. Disruptions constructed in the pleD open reading frame demonstrated that the gene is not essential and that the pleC ph enotype can also be suppressed by a recessive, loss-of-function mutati on. These results suggest that PleD is part of a signal transduction p athway controlling stalked-cell differentiation early in the C. cresce ntus cell cycle.