Characterization of the spoIVB and recN loci of Bacillus subtilis

Abstract

Two independent genes, recN and spoIVB, along with their respective promoter and termination regions, were discovered and sequenced in the 3.4-kilobase region between the ahrC and spoOA genes at map position 216 in the Bacillus subtilis chromosome map. The gene encoding a 576-amino-acid protein, which maintains a high homology with Escherichia coli recN gene product, was adjacent to ahrC. The sequence revealed a 64,472-dalton polypeptide which contained a conserved ATP-binding site and possible lexA-type regulatory binding sequences in its promoter region. A second open reading frame identified as the spoIVB gene was directly downstream of recN. It consisted of 1,275 nucleotides which coded for a 425-amino-acid polypeptide with a molecular weight of 45.976. Phenotypic, genetic, and transcriptional analyses confirmed that this gene was spoIVB. Although no chloroform-resistant spores were produced by spoIVB-inactivated strains, under microscopic examination, phase-gray forespores were visible. The spoIVB165 mutation was localized to a 200-base-pair region in the amino-terminal portion of the polypeptide. spoIVB was not transcribed until hour 2 of sporulation in wild-type B. subtilis cells, as determined by β-galactosidase activity assays from lacZ transcriptional fusion constructions. We found no amino acid sequence homology between the spoIVB gene product and other known bacterial proteins.