Chemotactic transducer proteins of Escherichia coli exhibit homology with methyl-accepting proteins from distantly related bacteria.

Transducers are transmembrane, methyl-accepting proteins central to the chemotactic systems of the enteric bacteria Escherichia coli and Salmonella typhimurium. Methyl-accepting proteins have been reported in a number of species in addition to these enteric bacteria. Those species include Bacillus subtilis and Spirochaeta aurantia, representatives of groups that diverged from ancestral enteric bacteria and from each other very early in bacterial evolution. An antiserum that reacts with all transducers of E. coli precipitated specifically methyl-accepting proteins from B. subtilis and S. aurantia, indicating that these proteins share antigenic determinants with transducers of E. coli. In addition, analysis of tryptic peptides by high-pressure liquid chromatography revealed similarities in the regions of methyl-accepting sites for proteins from all three species. These observations imply that structural features have been preserved in the three species from transducers contained in a common ancestor of eubacteria. It is thus reasonable to predict that other flagellated, chemotactic bacteria will be found to contain methyl-accepting proteins homologous to transducers of enteric bacteria.