REEXAMINATION OF THE VOLE 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 re gulatory protein, OmpR. OmpR-phosphate regulates the expression of the porin genes, ompF and ompC. To investigate the role of the periplasmi c domain of EnvZ in sensing of osmolarity signals, portions of this do main were deleted. Cells containing the EnvZ mutant proteins were able to regulate normally the production of OmpF and OmpC in response to c hanges in osmolarity. The periplasmic domain of EnvZ was also replaced with the non-homologous periplasmic domain of the histidine kinase Ph oR of Bacillus subtilis. Osmoregulation of OmpF and OmpC production in cells containing the PhoR-EnvZ hybrid protein was indistinguishable f rom that in cells containing wild-type EnvZ. Identical results were ob tained with an envZ-pta/ack strain, which could not synthesize acetyl phosphate. Thus, acetyl phosphate was not involved in the regulation o f ompF and ompC observed in this study. These results indicate that th e periplasmic domain of EnvZ is not essential for sensing of osmolarit y signals.