Bacillus subtilisgene coding for constitutiveO6-methylguanine-DNA alkyttransferase

We have cloned a Bacillus subtilis DNA fragment that could correct the defect in a constitutive O6-methylguanine-DNA alkyltransferase (Dat1). This fragment also corrected the hypersensitivity of the strain TKJ6951(ada-1 dat-1) to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). In the fragment, the gene activity resides in a region of about 850 bp which contains an open reading frame capable of coding for a protein of 165 amino acid residues. The amino acid sequence of this protein exhibits striking similarity to those of E. coli O6-methylguanine-DNA alkyltransferases (Ogt and Ada proteins). We conclude that this is a structural gene for the Dat1 protein, which is distinct from inducible DNA alkyltransferases involved in the adaptive response. The dat-1 mutation was shown to be caused by a structural rearrangement affecting the coding region, and the 0.8 kb transcripts of this gene were detected in dat+ cells but not in dat mutant cells.