Re-examination of the role of the periplasmic domain of EnvZ in sensing of osmolarity signals in Escherichia coli.

In Escherichia coli, EnvZ senses changes in the osmotic conditions of the growth environment and controls the phosphorylated state of the regulatory protein, OmpR. OmpR-phosphate regulates the expression of the porin genes, ompF and ompC. To investigate the role of the periplasmic domain of EnvZ in sensing of osmolarity signals, portions of this domain were deleted. Cells containing the EnvZ mutant proteins were able to regulate normally the production of OmpF and OmpC in response to changes in osmolarity. The periplasmic domain of EnvZ was also replaced with the non-homologous periplasmic domain of the histidine kinase PhoR of Bacillus subtilis. Osmoregulation of OmpF and OmpC production in cells containing the PhoR-EnvZ hybrid protein was indistinguishable from that in cells containing wild-type EnvZ. Identical results were obtained with an envZ-pta/ack strain, which could not synthesize acetyl phosphate. Thus, acetyl phosphate was not involved in the regulation of ompF and ompC observed in this study. These results indicate that the periplasmic domain of EnvZ is not essential for sensing of osmolarity signals.