News and Publications

Kinase-Phosphatase Competition in Bacterial Development

M. Perego, M. Jiang

Recognition of the diverse signals involved in the initiation of sporulation is carried out by proteins that alter the level of phosphorylation of the Spo0A transcription factor. The pathway to Spo0A activation is a sequential series of phosphorylation and phosphotransfer reactions that occur in the multicomponent phosphorelay. The phosphorelay signal transduction system is the province of signal integration, and the multicomponent structure of the system provides multiple entries for regulatory signals that affect the final goal of producing the appropriate level of phosphorylated Spo0A (Spo0A~P). 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.

The Spo0E protein specifically dephosphorylates the Spo0A~P component of the phosphorelay, and 3 members of the Rap family of phosphatases specifically dephosphorylate the Spo0F~P intermediate. 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. After cleavage by a signal peptidase, this protein, PhrA, is exported from the cell as a 19 amino acid peptide, processed down to the carboxyl-terminal pentapeptide (ARNQT), and reimported through the oligopeptide transport system. Through in vivo and in vitro studies, we showed that the pentapeptide specifically and directly inhibits the phosphatase activity of RapA. 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. Although RapB does not appear to be controlled by a cognate Phr peptide, the activity of RapE is directly inhibited by a PhrE pentapeptide (SRNVT), which, unlike PhrA, is located 9 amino acids from the carboxyl-terminal end.

The Rap family of phosphatases consists of 11 chromosomal genes. The Rap proteins show 30--50% identities in amino acid residues, and 7 of the proteins are associated with a PhrA-like protein. Preliminary studies indicate that the remaining Rap phosphatases most likely have roles in processes other than sporulation that are controlled by 2-component signal transduction systems.

PUBLICATIONS

Cervin, M.A., Spiegelman, G.B., Raether, B., Ohlsen, K., Perego, M., Hoch, J.A. A negative regulator linking chromosome segregation to developmental transcription in Bacillus subtilis. Mol. Microbiol. 29:85, 1998.

Perego, M. Kinase-phosphatase competition regulates Bacillus subtilis development. Trends Microbiol. 6:366, 1998.

Perego, M. Self-signaling by Phr peptides modulates Bacillus subtilis development in cell-cell signaling in bacteria. In: Cell-Cell Signaling in Bacteria. Dunny, G., Winans, S.C. (Eds.). American Society for Microbiology, Washington, DC, in press.