CHEZ MUTANTS WITH ENHANCED ABILITY TO DEPHOSPHORYLATE CHEY, THE RESPONSE REGULATOR IN BACTERIAL CHEMOTAXIS

CheZ is a component of the chemotaxis signal-transduction pathway in E scherichia coli and Salmonella typhimurium. It is responsible for acce lerating dephosphorylation of CheY and thereby antagonizing the tumble -promoting activity of CheY. In the absence of functional CheZ, cells are non-chemotactic and tumble constantly. We characterized the effect s of two mutations in CheZ, R54C and V166G, that are unusual in that t hey cause cells to have a smooth swimming bias. These mutations were i solated as second-site suppressors of mutations in the switch complex responsible for regulating the direction of flagellar rotation (Yamagu chi, S., Aizawa, S.-I., Kihara, M. Isomura, M., Jones, C.J. and Macnab , R.M. (1986) J. Bacteriol. 168, 1172-1179). When produced at low leve ls in a DELTAcheZ host strain, CheZ R54C and CheZ V166G supported chem otaxis. However, when moderately overproduced they markedly inhibited chemotactic ability. In vitro studies revealed that these mutations en hanced the ability of CheZ to accelerate dephosphorylation of CheY. Th ese results are discussed in relation to the possible roles and intera ctions of CheZ in the chemotaxis system.