CHARACTERIZATION OF DNA-DAMAGE INDUCED BY GAMMA-RADIATION-DERIVED WATER RADICALS, USING DNA-REPAIR ENZYMES

Purpose: To characterize the DNA damage profiles due to gamma-radiatio n induced water radicals. Materials and methods: Double stranded (ds) Phi X174 DNA was irradiated in aqueous solution with gamma-rays under different gassing conditions (O-2, N2O or N-2) and the damage profiles were determined using DNA repair enzymes. Results: The DNA damage pro file under O-2 is characterized by about equal numbers of direct singl e-strand breaks (ssb) and Fpg sensitive sites, whereas endonuclease II I and exonuclease III sites are formed in lower amounts. The DNA damag e profiles under N2O and N-2 in phosphate buffer consist predominantly of direct single-strand breaks. Fpg sensitive sites dominate the DNA damage profile under N-2 in phosphate buffer in the presence of the ra dical scavenger 2-methyl propan-2-ol, where (almost) only . H atoms ar e present. Conclusions: 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 an d . H atoms, but when both types of radicals are present, the formatio n of Fpg sensitive sites is prevented. Hydrated electrons (e(aq)(-)) c ontribute to inactivation of DNA, although only a very small fraction of the e(aq)(-) is involved in this process.