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Recruitment of a cytoplasmic response regulator to the cell pole is linked to its cell cycle-regulated proteolysis
Kathleen R. Ryan *,
Sarah Huntwork, and
Department of Developmental Biology, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine, Stanford, CA 94305
Contributed by Lucy Shapiro, March 29, 2004
The response regulator CtrA, which silences the Caulobacterorigin of replication and controls multiple cell cycle events,is specifically proteolyzed in cells preparing to initiate DNAreplication. At the swarmer-to-stalked cell transition and inthe stalked compartment of the predivisional cell, CtrA is localizedto the cell pole just before its degradation. Analysis of therequirements for CtrA polar localization and CtrA proteolysisrevealed that both processes require a motif within amino acids1-56 of the CtrA receiver domain, and neither process requiresCtrA phosphorylation. These results strongly suggest that CtrApolar localization is coupled to its cell cycle-regulated proteolysis.The polarly localized DivK response regulator promotes CtrAlocalization and proteolysis, but it does not directly recruitCtrA to the cell pole. Mutations in the divJ and pleC histidinekinases perturb the characteristic asymmetry of CtrA localizationand proteolysis in the predivisional cell. We propose that polarrecruitment of CtrA evolved to ensure that CtrA is degradedonly in the stalked half of the predivisional cell, perhapsby localizing a proteolytic adaptor protein to the stalked pole.This is an example of controlled proteolysis of a cytoplasmicprotein that is associated with its active recruitment to aspecific subcellular address.