The chromosomal region of Bacillus subtilis comprising the entire srfA operon, sfp and about four kilobases in between have been completely sequenced and functionally characterized. The srfA gene codes for three large subunits of surfactin synthetase, 402, 401 and 144 kDa, respectively, arranged in a series of seven amino acid activating domains which, as shown in the accompanying communication, recognize and bind the seven amino acids of the surfactin peptide. The srfA amino acid activating domains share homologies with similar domains of other peptide synthetases; in particular, regions can be identified which are more homologous in domains activating the same amino acid. A fourth gene in srfA encodes a polypeptide homologous to grsT. Four genes are positioned between srfA and sfp, the disruption of which does not affect surfactin biosynthesis.

It has been hypothesized that the dinR gene product of Bacillus subtilis acts as a repressor of the SOS regulon by binding to DNA sequences located upstream of SOS genes, including dinR and recA. Following activation as a result of DNA damage, RecA is believed to catalyse DinR-autocleavage, thus derepressing the SOS regulon. The present results support this hypothesis: a dinR insertion mutation caused a high, constitutive expression of both dinR and recA, which could not be further elevated by SOS-induction. In addition, gel-retardation assays demonstrated a direct interaction between the dinR gene product and the recA and dinR promoter regions. Epistatic interactions and gel-retardation assays demonstrated that the previously reported competence-specific expression of recA directly depended upon the gene product of comK, the competence transcription factor. These data demonstrate the existence of a direct regulatory link between the competence signal-transduction pathway and the SOS reguion.

Using the transformation-deficient mutant M465, which was previously isolated by means of insertional mutagenesis with plasmid pHV60, a transcription unit comL required for genetic competence of Bacillus subtilis was identified. A chromosomal DNA fragment flanking the inserted pHV60 was isolated and used to screen two different libraries of B. subtilis DNA in phage lambda EMBL4 and lambda EMBL12, respectively. With the aid of six recombinant phages that hybridize with this chromosomal fragment a restriction map of about 23 kb of B. subtilis chromosomal DNA was constructed. Using small adjoining pieces of this chromosomal DNA in Campbell integrations, the size of the transcription unit involved in competence development could be delimited to about 15 kb. By insertion of a promoterless lacZ gene into comL, the transcriptional regulation of comL was analysed and epistatic interactions among various other com genes were determined. The results of these experiments indicated that comL is optimally expressed in glucose-based minimal medium when the culture enters the stationary phase of growth and that the expression of late competence genes is dependent on previous transcription of comL, which in turn is dependent on the gene products of comA and comB.

Despite the lack of involvement of the competence-specific, membrane-associated deoxyribonuclease (DNase) in competence development, the expression of the gene encoding this protein, nucA, was shown to be dependent on the competence signal transduction pathway, and in particular on ComK, the competence transcription factor, which was shown to bind to the DNA region upstream of nucA. The expression of nucB, specifying an extracellular DNase, which was cloned on the basis of its homology to nucA, was shown to be sporulation-specific and dependent on the gene products of spo0A and spoIIG, the latter constituting an operon responsible for the synthesis of the mother-cell-specific sigma factor sigma E. The observed differential expression of nucA and nucB demarcates the appearance of DNase activities which are either associated with the cytoplasmic membrane or secreted into the medium during different post-exponential growth-phase processes.