Repair of deaminated cytosine residues of DNA: biological significance of the absence of uracil from DNA.

Uracil-DNA glycosylase of $\text{Bacillus}\text{subtilis}$ is involved in repair of deaminated cytosine residues of DNA. Survivals of SPO2 phage after treatment with bisulfite and weak alkali are considerably higher in wild type strains than in $\text{urg}$ mutants, which are deficient in the enzyme activity, whereas survivals of bisulfite/alkali-treated PBS1 phage in the two types of cells are essentially the same. The spontaneous mutation frequency of a $\text{urg}$ mutant is three fold higher than is that of a wild type strain.