REGULATORY INPUTS FOR THE SYNTHESIS OF COMK, THE COMPETENCE TRANSCRIPTION FACTOR OF BACILLUS-SUBTILIS

Competence in Bacillus subtilis is expressed post-exponentially in res ponse to signals which are interpreted by a complex network of regulat ory proteins. This network culminates in the transcriptional activatio n of a set of late-competence proteins that mediate DNA binding and up take during transformation. ComK, a protein that binds to competence p romoters and appears to activate their transcription, is itself synthe sized in response to the signal-transduction network. ComK is known to be required for the transcription of its own gene. We have placed com K under control of the xylose-inducible PxylA promoter and used this c onstruct to show that ComK synthesis is sufficient as well as necessar y to induce competence. We have also confirmed that the Mec proteins a ct posttranscriptionally to inactivate ComK, probably by protein-prote in interaction. We have further demonstrated that ComS is required to generate an upstream signal that causes reversal of Mec-induced inacti vation of ComK. In addition to ComK itself, DegU, AbrB, and SinR are r equired for comK transcription; mutations in their genes are bypassed by PxylA-comK induction, and therefore their products appear not to ac t via the Mec proteins. Overproduction of ComK, in a loss-of-function mec mutant, is also known to bypass the need for DegU, SinR and AbrB. We propose that these proteins enhance the activity of ComK as a posit ive autoregulatory transcription factor, acting as coactivator protein s when ComK is present at low concentrations. Finally, we demonstrate that when ComK is synthesized from the PxylA promoter and mecA is inac tivated by mutation, no additional growth-stage-regulated control of c ompetence can be detected.