Prokaryotes can modulate gene expression in response to changes in external osmolarity through a two-component phosphorelay signaling system that involves a transmembrane histidine kinase called EnvZ. EnvZ also has phosphatase activity, and so it can both phosphorylate and dephosphorylate a transcription factor called OmpR. Qin et al. report that the presence of DNA fragments corresponding to the promoter regions of OmpR-regulated genes caused a reduction in the apparent phosphatase activity of EnvZ in vitro. Biochemical analysis of complexes formed in vitro suggests that DNA binds to phosphorylated OmpR and sequesters it from phosphatase action of EnvZ. This finding offers an alternative for earlier results interpreted to show that EnvZ kinase activity can be enhanced by DNA and leaves open the question of how the dual enzymatic activity of EnvZ is regulated in vivo.
L. Qin, T. Yoshida, M. Inouye, The critical role of DNA in the equilibrium between OmpR and phosphorylated OmpR mediated by EnvZ in Escherichia coli. Proc. Natl. Acad. Sci. U.S.A. 98: 908-913 (2001). [Abstract] [Full Text]