Effects of transition mutations in the regulatory locus spoIIA on the incidence of sporulation in Bacillus subtilis.

We have determined the changes in DNA sequence corresponding to three mutations in the promoter-proximal open reading frame of spoIIA, a locus that regulates sporulation in Bacillus subtilis. All three mutations prevent the synthesis of two sporulation-associated enzymes, but they differ in their effects on spore incidence. We now find that mutation spo-42, which allows spores to be produced at a low incidence, is a transition that changes Gly95 to Asp in the protein encoded by the open reading frame. Mutation spo-69, which blocks sporulation entirely, consists of two transitions: these change Gly62 to Asp and Ala1 16 to Thr. Mutation sas-1, which partially suppresses spo-69, is also a transition: this changes residue 62 (which had become Asp as a result of the spo-69 mutation) to Asn.