A homolog of the CtrA cell cycle regulator is present and essential in Sinorhizobium meliloti

During development of the symbiotic soil bacterium Sinorhizobium meliloti i nto 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 identifie d, 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 regu lators found in several cu-proteobacteria, In Caulobacter crescentus, CtrA is essential and Is a global regulator of multiple cell cycle functions, et r,l 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 pr omoter regions which bind phosphorylated CtrA.