Bacillus subtilis ComK negatively regulates degR gene expression

Exoprotease production in Bacillus subtilis is positively regulated by a two-component regulatory system, DegS-DegU, and, in addition, by several minor factors. The product of the degR gene belongs to the latter group and exerts a positive effect in a DegS-DegU dependent manner. We found that transcription of degR was prevented by disruption of either mecA or mecB but was relieved by further disruption of comK. Disruption of comK alone, however, did not alter degR transcription. We also found that the mecA mutation requires a region around position −52 relative to the transcription start point of degR to exert its effect. We have shown previously that the transcription of degR is driven by an alternative sigma factor, σD. When degR expression was directed by an artificially constructed σA-type promoter, disruption of mecA/B did not result in any significant decrease in degR expression, indicating that the negative effect of the mec mutations acts through σD-driven transcription. It has been demonstrated that MecA and MecB negatively regulate ComK, and mecA/B null mutations cause enhanced expression of comK. From these results we conclude that ComK negatively regulates degR expression by preventing σD-driven transcription of degR, possibly through interaction with the control region.