Formation of novel C-1-oxidised abasic sites in alkylperoxyl radical-damaged plasmid DNA

We have recently shown that peroxyl radicals react with DNA to form alkali-labile sites. To further characterise these lesions, we studied their susceptibility to digestion by repair endonucleases that recognise different types of abasic sites. We found that peroxyl radical-damaged pSP189 plasmids were resistant to cleavage by T4 endonuclease V, an enzyme that incises DNA at ''regular'' and C-4-oxidised abasic residues. In contrast, the DNA was digested by exonuclease III, an enzyme that recognises ''regular'' and C-1-oxidised abasic sites. The presence of Trolox during exposure to peroxyl radicals reduced subsequent DNA cleavage by exonuclease III, while prior incubation of damaged plasmids with methoxyamine potentiated digestion by this enzyme. These findings suggest that peroxyl radical-induced DNA damage involves the generation of novel C-1-oxidised deoxyribose residues. (C) 1997 Academic Press.