Organization and nucleotide sequence of the Bacillus subtilis diaminopimelate operon, a cluster of genes encoding the first three enzymes of diaminopimelate synthesis and dipicolinate synthase

The nucleotide sequence of a 7-kilobase segment of the Bacillus subtilis chromosome containing the entire coding regions for the enzymes catalyzing the first three steps of diaminopimelate synthesis as well as dipicolinate synthase has been determined. This group of functionally related genes, termed the dap operon, were arranged in the order orfY, orfX, asd, dapG, and dapA and were bracketed by potential rho-independent transcription terminators. The asd locus could complement the growth defect of Escherichia coli strains with an asd deletion. Disruption of the dapG locus led to the loss of aspartokinase I, with a phenotype similar to that of the temperature-sensitive dapG mutants described earlier (Roten, C. A. H., Brandt, C., and Karamata, D. (1991) J. Gen. Microbiol. 137, 951-962). The amino acid sequences of the deduced products of the asd, dapG, and dapA loci had high degrees of similarity with those of other aspartate semialdehyde dehydrogenases, aspartokinases, and dihydrodipicolinate synthases, respectively. Disruption of orfX had no effect on growth but caused a sporulation defect, characterized by low sporulation frequencies and heat-sensitive spores, which could be cured by supplementation with dipicolinate, similar to the phenotype of mutants defective in spoVF, the putative structural gene for dipicolinate synthase. Two other open reading frames, upstream of spoVF, encoded the 380 COOH-terminal residues of a protein homologous to mitochondrial processing proteases and an 85-residue polypeptide of unknown function. Transcription initiation sites associated with the orfY-orfX-asd-dapG-dapA gene cluster were mapped by primer extension. The results indicate that during vegetative growth, the three distal genes of the dap operon, asd, dapG, and dapA, are transcribed as a unit and orfY and orfX are not expressed, whereas at stage 5 of sporulation two separate transcripts are produced, one comprising all five genes, the other just the three distal genes of the operon.