Ordered methylation of the methyl-accepting chemotaxis proteins of Escherichia coli

The methylation of glutamic acid residues on 3 membrane proteins, MCPI, MCPII, and MCPIII, plays an essential role in the chemotactic response of Escherichia coli. In the absence of a chemotactic stimulus the methyl-accepting chemotaxis proteins (MCPs) are methylated to a basal level. This level rises to a new plateau when an attractant is added and then falls to its original basal value when the attractant is removed. We have now been able to show that the properties of the glutamic acid residues which become methylated after stimulation with an attractant differ from the properties of the residues methylated on the basal level. Our data imply that there is a preferred order in which those residues are methylated and demethylated.