A NOVEL ACTIVITY OF ESCHERICHIA-COLI URACIL DNA N-GLYCOSYLASE EXCISION OF ISODIALURIC ACID (5,6-DIHYDROXYURACIL), A MAJOR PRODUCT OF OXIDATIVE DNA-DAMAGE, FROM DNA

We describe a novel activity of E. coli uracil DNA N-glycosylase (UNG) that excises isodialuric acid from DNA, Isodialuric acid is formed in DNA as a major oxidative product of cytosine, DNA substrates, which w ere prepared by gamma-irradiation, were incubated with UNG. Following precipitation of DNA, analyses of pellets and supernatant fractions by gas chromatography/mass spectrometry showed an efficient excision of isodialuric acid from DNA by UNG. None of the other 15 identified DNA base lesions was excised, The excision of isodialuric acid indicates t hat the non-aromaticity of a substrate may not be a limiting factor fo r UNG.