Molecular cloning and sequence of comK, a gene required for genetic competence in Bacillus subtilis

The transformation-deficient strain E26, isolated as a pHV60 insertion mutant, was used to isolate comK, a novel transcription unit required for genetic competence in Bacillus subtilis. Mutational analysis and sequence determination showed that comK contained one open reading frame (ORF), which could encode a protein of 192 amino acid residues with a predicted molecular weight of 22,500. An integrated copy of comK not only complemented the competence deficiency of a comK deletion mutant, but also that of strains E26 and FB93. Expression of comK occurred exclusively in glucose-based minimal medium during the transition to stationary growth phase. Furthermore, the expression of late competence genes appeared to be dependent on the gene product of comK, the expression of which in turn depended on the presence of a functional comL (or srfA) transcription unit. These epistatic interactions indicate that comK is a competence locus occupying an intermediate position in the competence signal transduction network. Primer extension analysis showed that comK has one major transcription start site, preceded by a sequence resembling the consensus promoter used by the sigma A form of RNA polymerase.