IDENTIFICATION OF FLAGELLAR SYNTHESIS REGULATORY AND STRUCTURAL GENESIN A SIGMA(D)-DEPENDENT OPERON OF BACILLUS-SUBTILIS

The sigma(D) form of RNA polymerase from Bacillus subtilis has been sh own previously to direct the synthesis of several transcription units bearing genes for flagellin, motility proteins, and autolysins. In thi s report, we describe an operon of genes transcribed from the sigma(D) -dependent promoter P-D-1. We have identified three complete open read ing frames and one partial one downstream of this promoter; immediatel y upstream is the previously identified comF locus. The P-D-1 operon e ncodes the presumptive B. subtilis homologs of two Salmonella typhimur ium late flagellar genes, flgM and flgK. Also present in this operon a re two genes of unknown function, orf139 and orf160, whose products sh ow similarities to the eukaryotic cytoskeletal proteins myosin and vim entin, respectively. orf139 and orf160 may encode proteins that form e xtended alpha-helical secondary structures and coiled-coil quaternary structures which may be filamentous components of the gram-positive ba cterial flagellum. We have characterized the B. subtilis flgM gene fur ther by constructing an in-frame deletion mutation, flgM Delta 80, and creating strains of B. subtilis in which this allele has replaced the wild-type copy. By primer extension analysis of cellular RNA, we have shown that the flgM Delta 80 mutation relieves the block to transcrip tion of two other sigma(D)-dependent operons imposed by an unlinked mu tation in a gene directing early flagellar synthesis. We conclude that , as in the case of S. typhimurium, early flagellar synthesis in B. su btilis is coupled to late flagellar synthesis through repression of si gma(D)-dependent transcription by the flgM gene product.