An enzyme activity specific for nitrous acid-treated DNA in Escherichia coli

An enzyme activity specifically active on nitrous acid-treated DNA was found in an extract of Escherichia coli. The enzyme acts on both double- and single-stranded DNAs, treated with nitrous acid, in the presence of EDTA, although the former DNA is a better substrate. Evidence is presented that nitrous acid- and bisulfite-induced types of damage in DNA are recognized by different enzymes: (1) Uracil-DNA glycosylase, purified 250-fold from E. coli 1100, attacks bisulfite-treated DNA but not nitrous acid-treated DNA. (2) Almost equal levels of activity toward nitrous acid-treated DNA were found in wild-type and uracil-DNA glycosylase-deficient strains of E. coli.