Involved in the transmission of sensory signals from the chemoreceptors to the flagellar motors. In its active (phosphorylated or acetylated) form, CheY exhibits enhanced binding to a switch component, FliM, at the flagellar motor which induces a change from counterclockwise to clockwise flagellar rotation. Shows autophosphatase activity which is enhanced by CheZ. Binds 1 Mg(2+) ion per subunit. Interacts (phosphorylated CheY) with CheZ (via C-terminus). Phosphorylated by CheA or acetylated by acetyl-CoA synthetase, depending on which acetate metabolism pathway is available (By similarity). Dephosphorylated (inactivated) by CheZ.