THE SHORT FORM OF THE CHEA PROTEIN RESTORES KINASE-ACTIVITY AND CHEMOTACTIC ABILITY TO KINASE-DEFICIENT MUTANTS

Escherichia coli expresses two forms of the chemotaxis-associated CheA protein, CheA(L) and CheA(S), as the result of translational initiation at two distinct, in-frame initiation sites in the gene cheA. The long form, CheA(L), plays a crucial role in the chemotactic signal transduction mechanism by phosphorylating two other chemotaxis proteins: CheY and CheB. CheA(L) must first autophosphorylate at amino acid His-48 before transferring its phosphono group to these other signal transduction proteins. The short form, CheA(S), lacks the N-terminal 97 amino acids of CheA(L) and, therefore, does not possess the site of autophosphorylation. Here we demonstrate that although it lacks the ability to autophosphorylate, CheA(S) can mediate phosphorylation of kinase-deficient variants of CheA(L) each of which retains a functional autophosphorylation site. This transphosphorylation enables these kinase-deficient CheA(L) variants to phosphorylate CheY. Because it mediates this activity, CheA(S) can restore to kinase-deficient E. coli cells the ability to tumble and, thus, to perform chemotaxis in swarm plate assays.