ROLE OF HIS243 IN THE PHOSPHATASE-ACTIVITY OF ENVZ IN ESCHERICHIA-COLI

EnvZ undergoes autophosphorylation at His243 and subsequently transfer s the phosphate group to OmpR. EnvZ also possesses an OmpR-phosphate p hosphatase activity. We examined the role of His243 in the phosphatase function by replacing His with either Val, Tyr, Ser, Asp, or Asn. Env ZH243V and EnvZH243Y were both shown to possess phosphatase activity i n vitro. In addition, the mutant proteins were able to reduce the high level of OmpR-phosphate present in the envZ473 strain. These results indicate that His243 of EnvZ is not essential for stimulating the deph osphorylation of OmpR-phosphate.