Sequence and transcription mapping of Bacillus subtilis competence genes comB and comA, one of which is related to a family of bacterial regulatory determinants

Abstract

The complete nucleotide sequences of the comA and comB loci of Bacillus subtilis were determined. The products of these genes are required for the development of competence in B. subtilis and for the expression of late-expressing competence genes. The major 5' termini of both the comA and comB transcripts were determined. The inferred promoters of both comA and comB contained sequences that were similar to those found at the -10 and -35 regions of promoters that are used by sigma A-RNA polymerase, the primary form of this enzyme in vegetative cells. The comB gene was located approximately 3 kilobase pairs upstream of the comA gene and encoded a 409-amino-acid protein with a predicted molecular weight of 46,693. The comA locus contained two open reading frames (ORFs) and comB contained one ORF. The predicted amino acid sequence of the comA ORF1 gene product consisted of 214 amino acids, with an aggregate molecular weight of 24,132. The ORF1 product was required for competence, while ORF2, which was cotranscribed with ORF1 and encoded a predicted protein of 126 amino acids, was not. The predicted protein sequence of the comA ORF1 gene product was found to be similar to that of several members of the effector class of procaryotic signal transducers. The C-terminal portion of the predicted comA sequence contained a possible helix-turn-helix motif, which is characteristic of DNA-binding proteins. comA ORF1 was cloned on a multicopy plasmid and was shown to complement the competence-deficient phenotype caused by the comA124 insertion of Tn917lac. Also, the presence of comA ORF1 in multiple copies interfered with sporulation. Anti-peptide antibodies raised to the predicted product of comA ORF1 reacted strongly with a single protein band of about 24,000 daltons in immunoblots. The possible roles of multiple signal transduction systems in triggering the development of competence are discussed.