Characterization of DNA damage induced by gamma-radiation-derived water radicals, using DNA repair enzymes

To characterize the DNA damage profiles due to gamma-radiation induced water radicals. Double stranded (ds) phiX174 DNA was irradiated in aqueous solution with gamma-rays under different gassing conditions (O2, N2O or N2) and the damage profiles were determined using DNA repair enzymes. The DNA damage profile under O2 is characterized by about equal numbers of direct single-strand breaks (ssb) and Fpg sensitive sites, whereas endonuclease III and exonuclease III sites are formed in lower amounts. The DNA damage profiles under N2O and N2 in phosphate buffer consist predominantly of direct single-strand breaks. Fpg sensitive sites dominate the DNA damage profile under N2 in phosphate buffer in the presence of the radical scavenger 2-methyl propan-2-ol, where (almost) only .H atoms are present. Both .OH radicals and .H atoms induce direct single-strand breaks, but .OH radicals are the most effective ones. Fpg sensitive sites are induced in high amounts by both .OH radicals and H atoms, but when both types of radicals are present, the formation of Fpg sensitive sites is prevented. Hydrated electrons (e(aq)-) contribute to inactivation of DNA, although only a very small fraction of the e(aq)- is involved in this process.