Receptor interactions through phosphorylation and methylation pathways in bacterial chemotaxis.

The effects of messages initiated by one receptor on the covalent modification of a second receptor were studied by use of a technique for rapidly separating the receptors. Methylation of the bacterial-chemotactic serine receptor increases as a result of aspartate binding to the aspartate receptor. The aspartate-induced methylation on the serine receptor is absent in a strain that lacks cheA and cheW genes and is not the result of physical interaction, such as the formation of heterodimers between the aspartate and serine receptors, or of alterations in the affinity of the serine receptor for the methyltransferase and the methylesterase. Serine-induced methylation of the serine receptor did not require cheA and cheW. A model is presented in which the receptor methylation level depends on the combination of (i) a ligand-induced conformational change on the receptor substrate of the methylation enzymes and (ii) an indirect cytoplasmic signal that operates through the methylesterase.