Abstract
Despite the myriad of different sensory domains encoded in bacteria, only a few types are known to control the cell cycle. Here we use a forward genetic screen for Caulobacter crescentus motility mutants to identify a conserved single-domain PAS (Per-Arnt-Sim) protein (MopJ) with pleiotropic regulatory functions. MopJ promotes re-accumulation of the master cell cycle regulator CtrA after its proteolytic destruction is triggered by the DivJ kinase at the G1-S transition. MopJ and CtrA syntheses are coordinately induced in S-phase, followed by the sequestration of MopJ to cell poles in Caulobacter. Polarization requires Caulobacter DivJ and the PopZ polar organizer. MopJ interacts with DivJ and influences the localization and activity of downstream cell cycle effectors. Because MopJ abundance is upregulated in stationary phase and by the alarmone (p)ppGpp, conserved systemic signals acting on the cell cycle and growth phase control are genetically integrated through this conserved single PAS-domain protein.
Highlights
Despite the myriad of different sensory domains encoded in bacteria, only a few types are known to control the cell cycle
Caulobacter divides asymmetrically into a swarmer cell that resides in a G1-like quiescent state and harbours the flagellum and several pili at the same cell pole, and a replicative (S-phase) cell whose old cell pole is decorated by a cylindrical extension of the cell envelope tipped by an adhesive holdfast (Fig. 1a)[2]
Orthologues of MopJ are encoded in the genomes of distantly related a-Proteobacteria (Supplementary Fig. 1) such as the animal pathogen Brucella melitensis (BMEI0738), the plant pathogen Agrobacterium tumefaciens (Atu1754) and the plant symbiont Sinorhizobium meliloti (SMc01000)
Summary
Despite the myriad of different sensory domains encoded in bacteria, only a few types are known to control the cell cycle. MopJ promotes re-accumulation of the master cell cycle regulator CtrA after its proteolytic destruction is triggered by the DivJ kinase at the G1-S transition. Cellular motility is responsive to external signals such as nutritional changes, but it is regulated by cues induced systemically during each cell division cycle[1,2]. The DNA-binding activity of RRs such as CtrA is regulated by phosphorylation at a conserved (Asp) residue, a step that is often executed directly by a histidine kinase (HK)[7]. At the G1-S transition, DivJ is recruited to the stalked pole by its localization factor SpmX, an event that is required for optimal DivJ kinase activity in vivo[3,31,32]. The sequestration of DivK to the stalked pole is governed by DivJ, even in the absence of kinase activity[17]
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