CHARACTERIZATION OF THE CHEA(S) CHEZ COMPLEX - A SPECIFIC INTERACTIONRESULTING IN ENHANCED DEPHOSPHORYLATING ACTIVITY ON CHEY-PHOSPHATE/

The cheA gene encodes two overlapping polypeptides with a common carbo xyl terminus: CheA(L) and CheA(S). CheA(L) plays a central role in the Escherichia coil chemotaxis signalling pathway by autophosphorylation and transferring the phosphate to both CheY and CheB. On the other ha nd, the physiological functions of CheA(S) remain unknown. We have obs erved that overproduction of CheA(S) in wild-type cells increased coun terclockwise-biased flagellar rotation, and this effect is dependent o n the presence of CheZ. CheZ specifically facilitates CheY-phosphate ( CheY-P) dephosphorylation and generates a smooth swimming signal. A ph ysical interaction was detected between CheZ and CheA(S) in wild-type cell lysates by immunoprecipitation. The CheA(S)/CheZ interaction does not require other chemotaxis components, as we could form the complex using purified CheA(S) and CheZ proteins. The ability of CheA(S) to b ind to CheZ depends on its being in the reduced state. We found that u nder non-reducing conditions, CheA(S) appears to form intermolecular d isulphide bonds and loses the ability to bind to CheZ. Finally, the Ch eA(S)/CheZ complex formed in vitro shows a greater dephosphorylating a ctivity on CheY-P than does free CheZ.