The pleiotropic response regulator DegU functions as a priming protein in competence development in Bacillus subtilis

The response regulator DegU is involved in various late-growth developmenta l processes in Bacillus subtilis, including the production of degradative e nzymes and the development of genetic competence. DegU is essential for the expression of the competence transcription factor, encoded by comK, ComK i s required for the transcription of genes encoding the DNA uptake and integ ration machinery, as well as for the transcription of its own gene. We have purified DegU to study its role in the expression of comK, and we demonstr ate here that DegU binds specifically to the comK promoter. The binding of the response regulator DegU to a promoter target had not been reported prev iously. DNase I protection analyses show that the DegU binding site overlap s with the ComK binding site, and gel retardation experiments indicate that DegU strongly stimulates the binding of ComK to the comK promoter. We prop ose that DegU functions at the initiation of competence development, when C omK concentrations are insufficient to support comK transcription, by facil itating ComK binding to the comK promoter. DegU therefore acts as a priming protein that primes the autostimulatory transcription of comK. Such primin g activity adds a function to the class of response regulator proteins.