Molecular and phenotypic characterization of promoter-proximal mutations in the spoIIA locus of Bacillus subtilis.

Abstract

Eight mutations lying within the promoter-proximal one-fifth of the spoIIA locus of Bacillus subtilis were studied. Two of these mutations (spoIIAA42 and spoIIAA69) were previously characterized at the DNA level, five more (spo-562, spo-565, spo-567, spo-568, and spo-569) were isolated in our laboratory several years ago but not fully characterized, and the eight (an in-frame deletion confined to spoIIAA, the first gene in the spoIIA operon) was constructed for this study. DNA sequencing showed that spo-569 was a transitions in the -35 region of the spoIIA promoter; the remaining point mutations were all G:C to A:T transitions in spoIIAA, with spo-565 having two transitions, one of which was identical to that in spo-562. All the spoIIAA mutations except spo-562 led to the replacement of Gly residues. The incidence of sporulation, the rate of synthesis of sporulation-associated alkaline phosphatase, and the rate of expression of the forespore-specific genes gpr and spoIIIG were determined for isogenic strains carrying the eight mutations. All the mutations except spoIIAA42 and spo-569 (which were slightly leaky) made the strains asporogenous, and all except spo-562 and spo-569 abolished the synthesis of alkaline phosphatase and the expression of gpr and spoIIIG. spo-562 allowed alkaline phosphatase synthesis and gpr and spoIIIG expression to occur at about 15% of the wild-type rates but with normal kinetics. spo-59 allowed appreciable gpr and spoIIIG expression during exponential growth; we attribute this expression to transcription by RNA polymerase containing sigma G and suggest that a spo-569 strain makes insufficient SpoIIAB to inhibit sigma G in growing cells.