A Homolog of the CtrA Cell Cycle Regulator Is Present and Essential in Sinorhizobium meliloti

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Abstract
During development of the symbiotic soil bacterium Sinorhizobium meliloti into nitrogen-fixing bacteroids, DNA replication and cell division cease and the cells undergo profound metabolic and morphological changes. Regulatory genes controlling the early stages of this process have not been identified. As a first step in the search for regulators of these events, we report the isolation and characterization of a ctrA gene from S. meliloti . We show that the S. meliloti CtrA belongs to the CtrA-like family of response regulators found in several α-proteobacteria. In Caulobacter crescentus , CtrA is essential and is a global regulator of multiple cell cycle functions. ctrA is also an essential gene in S. meliloti , and it is expressed similarly to the autoregulated C. crescentus ctrA in that both genes have complex promoter regions which bind phosphorylated CtrA.