Relative Roles of the fla/che P(A), P(D-3), and P(sigD) Promoters in Regulating Motility and sigD Expression in Bacillus subtilis

Three promoters have been identified as having potentially important regulatory roles in governing expression of the fla/che operon and of sigD, a gene that lies near the 3′ end of the operon. Two of these promoters, fla/che P(A) and P(D-3), lie upstream of the >26-kb fla/che operon. The third promoter, P(sigD), lies within the operon, immediately upstream of sigD. fla/che P(A), transcribed by Eς(A), lies ≥24 kb upstream of sigD and appears to be largely responsible for sigD expression. P(D-3), transcribed by Eς(D), has been proposed to participate in an autoregulatory positive feedback loop. P(sigD), a minor ς(A)-dependent promoter, has been implicated as essential for normal expression of the fla/che operon. We tested the proposed functions of these promoters in experiments that utilized strains that bear chromosomal deletions of fla/che P(A), P(D-3), or P(sigD). Our analysis of these strains indicates that fla/che P(A) is absolutely essential for motility, that P(D-3) does not function in positive feedback regulation of sigD expression, and that P(sigD) is not essential for normal fla/che expression. Further, our results suggest that an additional promoter(s) contributes to sigD expression.