We have observed that overproduction of CheAS in wild type cells increased counterclockwise biased flagellar rotation, and this effect is dependent on the presence of CheZ. CheZ specifically facilitates CheY-P dephosphorylation and generates a smooth swimming signal. A physical interaction was detected between CheZ and CheAS in wild type cell lysates by immunoprecipitation. The CheAS/CheZ interaction does not require other chemotaxis components, as we could form the complex using purified CheAS and CheZ proteins. The ability of CheAS to bind to CheZ depends on its being in the reduced state. We found that under non-reducing conditions, CheAS appears to form intermolecular disulfide bonds and loses the ability to bind to CheZ. Finally, the CheAS/CheZ complex formed in vitro shows a greater dephosphorylating activity on CheY-P than does free CheZ.
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