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Journal of Bacteriology, August 1998, p. 3765-3770, Vol. 180, No. 15
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Promoter Recognition by Bacillus subtilis sigma W: Autoregulation and Partial Overlap with the sigma X Regulon

Xuejun Huang, Kurt L. Fredrick,dagger and John D. Helmann*

Section of Microbiology, Cornell University, Ithaca, New York 14853-8101

Received 14 April 1998/Accepted 26 May 1998

The Bacillus subtilis genome encodes at least 17 distinct sigma factors, including seven members of the extracytoplasmic function (ECF) subfamily. We have investigated the expression and regulation of the ECF sigma  factor encoded by the sigW gene. A sigma W-dependent promoter (PW) precedes sigW, demonstrating that this transcription factor is positively autoregulated. Expression of sigW is regulated by both growth phase and medium composition. Maximal expression is attained in early-stationary-phase cells grown in rich medium. We previously reported that sigW mutants have elevated transcription of some sigma X-controlled genes, and we now report that the converse is also true: in a sigX mutant, PW is derepressed during logarithmic growth. Thus, these two regulons are mutually antagonistic. Reconstituted sigma W holoenzyme faithfully recognizes the PW preceding sigW but does not recognize the PX promoter preceding the sigX gene. Autoregulation of sigX is also highly specific: sigma X holoenzyme initiates transcription from PX but recognizes PW poorly if at all. In contrast, several promoters that are at least partially under sigma X control are active with both the sigma X and sigma W holoenzymes in vitro. This finding supports the suggestion that the sigma W and sigma X regulons overlap. Sequence comparisons suggest that promoters recognized by these two sigma  factors have similar -35 elements but are distinguished by different base preferences at two key positions within the -10 element.

* Corresponding author. Mailing address: Section of Microbiology, Wing Hall, Cornell University, Ithaca, NY 14853-8101. Phone: (607) 255-6570. Fax: (607) 255-3904. E-mail: jdh9{at}cornell.edu.

dagger Present address: Department of Microbiology, University of Minnesota, Minneapolis, MN 55455-0312.

Journal of Bacteriology, August 1998, p. 3765-3770, Vol. 180, No. 15
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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