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J. Bacteriol. doi:10.1128/JB.01497-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Genetic evidence for the actin homolog gene mreBH and the bacitracin resistance gene bcrC as targets of the alternative sigma factor SigI of Bacillus subtilis

Institute of Biochemistry and Molecular Biology, School of Life Science, National Yang-Ming University, Taipei, Taiwan, Republic of China

^* To whom correspondence should be addressed. Email: gcshaw{at}ym.edu.tw.

	Abstract

The Bacillus subtilis sigI gene, which is a member of class VI heat shock genes of the B. subtilis heat shock stimulon, encodes an alternative sigma factor whose regulon is poorly defined. In this report, by using a binary vector system, we showed that the B. subtilis SigI could drive expression of a transcriptional fusion between the sigI regulatory region from B. licheniformis, B. sp. NRRL B-14911, B. subtilis, or B. thuringiensis and the xylE reporter gene in B. subtilis. The transcriptional initiation sites of these fusions in B. subtilis were mapped by primer extension analyses. A putative consensus promoter sequence probably recognized by the B. subtilis SigI was thus deduced. Using a consensus sequence-based search procedure, we found putative ^I promoters preceding the actin homolog gene mreBH and the bacitracin resistance gene bcrC of B. subtilis. Overexpression of the B. subtilis sigI gene could specifically stimulate expressions of both mreBH promoter region-bgaB fusion and bcrC promoter region-bgaB fusion. Expressions of these two fusions at the amyE locus of B. subtilis chromosome were heat-inducible and SigI-dependent as revealed by the sigI gene disruption experiment. Primer extension analysis showed that the identified mreBH and bcrC transcriptional start sites were at appropriate distances from their ^I promoter elements. This further supports the notion that SigI can directly regulate mreBH and bcrC expressions. Taken together, these results strongly suggest that mreBH and bcrC are new members of SigI regulon.