“…Although R. sphaeroides lacks a CheZ homologue, each locus encodes homologues of the remaining proteins of the E. coli chemosensory pathway. The proteins of immediate relevance to this study are: CheA 1 , CheY 1 , CheY 2 , and CheY 5 encoded by cheOp 1 (18,20); CheA 2 , CheB 1 , and CheY 3 encoded by cheOp 2 (19); CheA 3 , CheA 4 , CheB 2 , and CheY 6 encoded by cheOp 3 (15); CheY 4 encoded in a separate genetic locus with the chemoreceptor McpG (21). Genetic studies have shown that, although CheA 2 , CheA 3 , CheA 4 , CheB 1 , CheB 2 , and CheY 6 are essential for chemotaxis (15,22,23), all of the proteins encoded by cheOp 1 have no detectable role in chemotaxis (18).…”