Identification of comS, a gene of the srfA operon that regulates the establishment of genetic competence in Bacillus subtilis

Genetic competence (the ability to internalize exogenous DNA) in Bacillus subtilis is dependent on a regulatory pathway that activates the expression of a battery of competence-specific genes. The srfA operon, encoding the subunits of surfactin synthetase, which catalyzes the nonribosomal synthesis of the peptide antibiotic surfactin, also functions in the competence regulatory pathway. The DNA encoding only one of the seven amino acid- activating domains of surfactin synthetase, the valine-activating domain (srfAB1), is necessary for competence. Deletion analysis revealed that a 569- bp fragment of srfAB1, fused to the srfA promoter, complements a srfA deletion mutation (ΔsrfA) with respect to competence. This fragment contains an open reading frame consisting of 46 amino acids (orf46), which is out of frame with srfAB1. A frameshift mutation in srfAB upstream of orf46 has no effect on competence but a frameshift and nonsense mutation in orf46 resulted in failure to complement the ΔsrfA mutation. These results indicate that orf46 encodes the srfA-associated competence regulatory factor. Computer- aided analysis of the putative orf46 product (ComS) shows similarity to the homeodomain of the POU domain class of eukaryotic transcriptional regulators.