Dual Promoters Are Responsible for Transcription Initiation of the fla/che Operon in Bacillus subtilis

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FONTE

American Society for Microbiology

RESUMO

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 ςD factor, sigD. Sequence and primer extension data demonstrate that a PA promoter immediately upstream of flgB, henceforth referred to as the fla/che PA, and the PD-3 promoter are active in vivo. Transcription from the PD-3 element is dependent on ςD activity and is regulated by the flagellum-specific negative regulator, FlgM. In a strain containing a deletion of fla/che PA (PAΔ), ςD protein was not detected, demonstrating that the fla/che PA 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 ςD protein, the PAΔ strain grows as long filaments and does not express a ςD-dependent hag::lacZ reporter construct. These phenotypes are indicative of a lack of sigD expression or complete inhibition of ςD activity by FlgM. However, ςD activity is found in a double mutant containing the PAΔ 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 ςD activity does exist in the PAΔ mutant but can be detected only in the presence of a null mutation in flgM. Therefore, normal expression of sigD may also involve another promoter(s) within the fla/che operon.

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