Identification of a methyl-accepting chemotaxis protein for the ribose and galactose chemoreceptors of Escherichia coli.

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Abstract
The ribose and galactose chemoreceptors of E. coli were previously identified as the ribose- and galactose-binding proteins. The discovery of a methyl-accepting chemotaxis protein that functions in the transfer of receptor signals from these 2 binding proteins to the flagella is reported. This protein is distinct from previously described methyl-accepting chemotaxis proteins. Its level of methylation is influenced by D-ribose, D-galactose and certain structural analogs of them. This methyl-accepting protein is required for chemotaxis toward those attractants; mutants in the trg gene, which do not methylate this protein, are devoid of taxis toward D-ribose, D-galactose and their analogs. Methylation of the methyl-accepting protein in response to each of these attractants requires the appropriate binding protein. The binding protein''s chemoreceptor function is required for such methylation, but its transport activity is not. Because the function of this methyl-accepting chemotaxis protein involves 2 of the best-characterized chemoreceptors, the discovery of this protein represents a promoting base for further study of the linkage between chemoreceptors and flagella in bacteria.