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Journal of Bacteriology, July 1999, p. 4081-4088, Vol. 181, No. 13
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

sigma K Can Negatively Regulate sigE Expression by Two Different Mechanisms during Sporulation of Bacillus subtilis

Bin Zhang,1 Paolo Struffi,2 and Lee Kroos1,2,*

Department of Biochemistry1 and Genetics Program,2 Michigan State University, East Lansing, Michigan 48824

Received 5 February 1999/Accepted 20 April 1999

Temporal and spatial gene regulation during Bacillus subtilis sporulation involves the activation and inactivation of multiple sigma subunits of RNA polymerase in a cascade. In the mother cell compartment of sporulating cells, expression of the sigE gene, encoding the earlier-acting sigma factor, sigma E, is negatively regulated by the later-acting sigma factor, sigma K. Here, it is shown that the negative feedback loop does not require SinR, an inhibitor of sigE transcription. Production of sigma K about 1 h earlier than normal does affect Spo0A, which when phosphorylated is an activator of sigE transcription. A mutation in the spo0A gene, which bypasses the phosphorelay leading to the phosphorylation of Spo0A, diminished the negative effect of early sigma K production on sigE expression early in sporulation. Also, early production of sigma K reduced expression of other Spo0A-dependent genes but not expression of the Spo0A-independent ald gene. In contrast, both sigE and ald were overexpressed late in development of cells that fail to make sigma K. The ald promoter, like the sigE promoter, is believed to be recognized by sigma A RNA polymerase, suggesting that sigma K may inhibit sigma A activity late in sporulation. To exert this negative effect, sigma K must be transcriptionally active. A mutant form of sigma K that associates with core RNA polymerase, but does not direct transcription of a sigma K-dependent gene, failed to negatively regulate expression of sigE or ald late in development. On the other hand, the negative effect of early sigma K production on sigE expression early in sporulation did not require transcriptional activity of sigma K RNA polymerase. These results demonstrate that sigma K can negatively regulate sigE expression by two different mechanisms, one observed when sigma K is produced earlier than normal, which does not require sigma K to be transcriptionally active and affects Spo0A, and the other observed when sigma K is produced at the normal time, which requires sigma K RNA polymerase transcriptional activity. The latter mechanism facilitates the switch from sigma E to sigma K in the cascade controlling mother cell gene expression.

* Corresponding author. Mailing address: Department of Biochemistry, Michigan State University, East Lansing, MI 48824. Phone: (517) 355-9726. Fax: (517) 353-9334. E-mail: kroos{at}pilot.msu.edu.

Journal of Bacteriology, July 1999, p. 4081-4088, Vol. 181, No. 13
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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