A NOVEL PROTEIN-KINASE THAT CONTROLS CARBON CATABOLITE REPRESSION IN BACTERIA

HPr(Ser) kinase is the sensor in a multicomponent phosphorelay system that controls catabolite repression, sugar transport and carbon metabo lism in Gram-positive bacteria. Unlike most other protein kinases, it recognizes the tertiary structure in its target protein, HPr, a phosph ocarrier protein of the bacterial phosphotransferase system and a tran scriptional cofactor controlling the phenomenon of catabolite repressi on. We have identified the gene (ptsK) encoding this serine/threonine protein kinase and characterized the purified protein product. Ortholo gues of PtsK have been identified only in bacteria. These proteins con stitute a novel family unrelated to other previously characterized pro tein phosphorylating enzymes. The Bacillus subtilis kinase is shown to be allosterically activated by metabolites such as fructose 1,6-bisph osphate and inhibited by inorganic phosphate. In contrast to wild-type B. subtilis, the ptsK mutant is insensitive to transcriptional regula tion by catabolite repression. The reported results advance our unders tanding of phosphorylation-dependent carbon control mechanisms in Gram -positive bacteria.