ORGANIZATION AND NUCLEOTIDE-SEQUENCE OF THE BACILLUS-SUBTILIS DIAMINOPIMELATE OPERON, A CLUSTER OF GENES ENCODING THE 1ST 3 ENZYMES OF DIAMINOPIMELATE SYNTHESIS AND DIPICOLINATE SYNTHASE

The nucleotide sequence of a 7-kilobase segment of the Bacillus subtil is chromosome containing the entire coding regions for the enzymes cat alyzing 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-indepen dent transcription terminators. The asd locus could complement the gro wth defect of Escherichia coli strains with an asd deletion. Disruptio n of the dapG locus led to the loss of aspartokinase I, with a phenoty pe 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 pro ducts of the asd, dapG, and dapA loci had high degrees of similarity w ith those of other aspartate semialdehyde dehydrogenases, aspartokinas es, and dihydrodipicolinate synthases, respectively. Disruption of orf X had no effect on growth but caused a sporulation defect, characteriz ed by low sporulation frequencies and heat-sensitive spores, which cou ld be cured by supplementation with dipicolinate, similar to the pheno type of mutants defective in spoVF, the putative structural gene for d ipicolinate synthase. Two other open reading frames, upstream of spoVF , encoded the 380 COOH-terminal residues of a protein homologous to mi tochondrial processing proteases and an 85-residue polypeptide of unkn own function. Transcription initiation sites associated with the orfY- orfX-asd-dapG-dapA gene cluster were mapped by primer extension. The r esults 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.