ANALYSIS OF A CHEMOTAXIS OPERON FROM RHODOSPIRILLUM-CENTENUM

A chemotaxis gene cluster from the photosynthetic bacterium Rhodospiri llum centenum has been cloned, sequenced, and analyzed for the control of transcription during swimmer-to-swarm cell differentiation, The fi rst gene of the operon (cheAY) codes for a large 108-kDa polypeptide w ith an amino-terminal domain that is homologous to CheA and a carboxyl terminus that is homologous to CheY, cheAY is followed by cheW, an ad ditional homolog of cheY, cheB, and cheR, Sequence analysis indicated that all of the che genes are tightly compacted with the same transcri ptional polarity, suggesting that they are organized in an operon. Cot ranscription of the che genes was confirmed by demonstrating through W estern blot analysis that insertion of a polar spectinomycin resistanc e gene in cheAY results in loss of cheR expression. The promoter for t he che operon was mapped by primer extension analysis as well as by th e construction of promoter reporter plasmids that include several dele tion intervals, This analysis indicated that the R. centenum che opero n utilizes two promoters; one exhibits a sigma 70-like sequence motif, and the other exhibits a sigma(54)-like motif, Expression of the che operon is shown to be relatively constant for swimmer cells which cont ain a single flagellum and for swarm cells that contain multiple later al flagella.