FIG 1.

Two-component pathway model of CtrA cell cycle regulation. The S. meliloti genome encodes many of the two-component regulators of CtrA that have been identified in C. crescentus (black font). However, there are several points of divergence between these two distantly related alphaproteobacteria. S. meliloti contains an additional DivJ/PleC-like histidine kinase, CbrA, that promotes DivK phosphorylation (blue font). Additionally, S. meliloti lacks the c-di-GMP receptor PopA that is required to regulate CtrA proteolysis in C. crescentus (green font). DivK-P and CtrA-P, phosphorylated DivK and CtrA, respectively.