Dual promoters are responsible for transcription initiation of the fla/che operon in Bacillus subtilis

The fla/che region contains more than 30 genes required for flagellar synthesis and chemotaxis in Bacillus subtilis, including the gene for the flagellum-specific sigma(D) factor, sigD, Sequence and primer extension data demonstrate that a P-A promoter immediately upstream of flgB, henceforth referred to as the fla/che P-A, and the PD-3 promoter are active in vivo. Transcription from the PD-3 element is dependent on sigma(D) activity and is regulated by the flagellum-specific negative regulator, FlgM. In a strain containing a deletion of fla/che P-A (P(A)Delta), sigma(D) protein was not detected, demonstrating that the fla/che P-A is necessary for wild-type expression of the sigD gene. Thus, sigD is part of the > 26-kb fla/che operon. Consistent with a lack of detectable sigma(D) protein, the P(A)Delta strain grows as long filaments and does not express a sigma(D)-dependent hag::lacZ reporter construct, These phenotypes are indicative of a lack of sigD expression or complete inhibition of sigma(D) activity by FlgM. However, sigma(D) activity is found in a double mutant containing the P(A)Delta and a null mutation in flgM. The double mutant no longer grows as long filaments, and expression of hag::lacZ is partially restored. These data demonstrate that a low level of sigma(D) activity does exist in the P(A)Delta mutant but can be detected only in the presence of a null mutation in flgM. Therefore, normal expression of sigD mag. also involve another promoter(s) within the fla/che operon.