Cells of Escherichia coli contain a protein-tyrosine kinase, Wzc, and a phosphotyrosine-protein phosphatase, Wzb

Two proteins of Escherichia coli, termed Wzc and Wzb, were analyzed for the ir capacity to participate in the reversible phosphorylation of proteins on tyrosine. First,Wzc was overproduced from its specific gene and purified t o homogeneity by affinity chromatography. Upon incubation in the presence o f radioactive ATP, it was found to effectively autophosphorylate. Two-dimen sional analysis of its phosphoamino acid content revealed that it was modif ied exclusively at tyrosine. Second,Wzb was also overproduced from the corr esponding gene and purified to homogeneity by affinity chromatography. It w as shown to contain a phosphatase activity capable of cleaving the syntheti c substrate p-nitrophenyl phosphate into p-nitrophenol and free phosphate. In addition, it was assayed on individual phosphorylated amino acids and ap peared to dephosphorylate specifically phosphotyrosine, with no effect on p hosphoserine or phosphothreonine. Such specificity for phosphotyrosine was confirmed by the observation that Wzb was able to dephosphorylate previousl y autophosphorylated Wzc. Together, these data demonstrate, for the first t ime, that E. coil cells contain both a protein-tyrosine kinase and a phosph otyrosine-protein phosphatase. They also provide evidence that this phospha tase can utilize the kinase as an endogenous substrate, which suggests the occurrence of a regulatory mechanism connected with reversible protein phos phorylation on tyrosine. From comparative analysis of amino acid sequences, Wzc was found to be similar to a number of proteins present in other bacte rial species which are all involved in the synthesis or export of exopolysa ccharides. Since these polymers are considered important virulence factors, we suggest that reversible protein phosphorylation on tyrosine may be part of the cascade of reactions that determine the pathogenicity of bacteria.