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Journal of Bacteriology, March 2001, p. 1921-1927, Vol. 183, No. 6
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.6.1921-1927.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

The -10 Region Is a Key Promoter Specificity Determinant for the Bacillus subtilis Extracytoplasmic-Function sigma  Factors sigma X and sigma W

Jian Qiu and John D. Helmann*

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

Received 22 September 2000/Accepted 20 December 2000

Transcriptional selectivity derives, in large part, from the sequence-specific DNA-binding properties of the sigma  subunit of RNA polymerase. There are 17 sigma  factors in Bacillus subtilis which, in general, recognize distinct sets of promoters. However, some sigma  factors have overlapping promoter selectivity. We hypothesize that the overlap between the regulons activated by the sigma X and sigma W factors can be explained by overlapping specificity for the -10 region: sigma X recognizes -10 elements with the sequence CGAC and sigma W recognizes CGTA, while both can potentially recognize CGTC. To test this model, we mutated the sigma X-specific autoregulatory site (PX), containing the -10 element CGAC, to either CGTC or GCTA. Conversely, the sigma W autoregulatory site (PW) was altered from CGTA to CGTC or CGAC. Transcriptional analyses, both in vitro and in vivo, indicate that changes to the -10 element are sufficient to switch a promoter from the sigma X to the sigma W regulon or, conversely, from the sigma W to the sigma X regulon, but context effects clearly play an important role in determining promoter strength. It seems likely that these subtle differences in promoter selectivity derive from amino acid differences in conserved region 2 of sigma , which contacts the -10 element. However, we were unable to alter promoter selectivity by replacements of two candidate recognition residues in sigma W.

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

Journal of Bacteriology, March 2001, p. 1921-1927, Vol. 183, No. 6
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.6.1921-1927.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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