The pathway to Spo0A activation is a sequential series of phosphorylation and phosphotransfer reactions that occur in the multicomponent phosphorelay. The opposing activities of kinases and phosphatases influence the output of the system in a manner similar to that found in eukaryotic signal transduction systems.
Protein phosphatases provide access to the phosphorelay for additional regulatory signals.
Although the mechanisms that regulate Spo0E are still unknown, we have determined that the expression of RapA, RapB, and RapE is under control of physiologic states that are alternatives to sporulation. The phosphatase activity of RapA, RapB, and RapE is also differentially regulated by effector molecules. Phosphatase activity of RapA is regulated by a cotranscribed gene, phrA, that encodes a 44 amino acid protein. The journey of the phrA gene product to its final pentapeptide form is defined as an export-import control circuit with the function of a timing device that coordinates alternative physiologic functions with the initiation of sporulation. The Rap family of phosphatases consists of 11 chromosomal genes.