Bacteriophage T4 particles are refractory to bisulfite mutagenesis

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Bisulfite-induced deamination of cytosine produces uracil, a thymine analog reported to be mutagenic both in vitro and in vivo. Although deamination of cytosine in DNA should produced G:C→A:T transitions, treating bacteriophage T4 particles with 0.9 M bisulfite at pH 5 at 37°C produced no more mutations than did the equivalent buffer without bisulfite. Lack of bisulfite mutagenicity is fully consistent with the reported resistance of 5-substituted cytosines to bisulfite-induced deamination, since T4 DNA contains glucosylated 5-hydroxymethylcytosine. However, bisulfite also failed to induced mutations in T4 particles whose DNA contained unmodified cytosine. The lack of mutagenesis persisted in E. coli hosts deficient in uracil glycosylase, an enzyme expected to participate in the repair of the putative bisulfite-generated uracil. Cytosine in T4 DNA may be largely protected from bisulfite attack within phage particles.