Production of DNA Strand Breaks by the Hydroxyl Radical

Summary

The circular covalently-closed double-stranded replicative intermediate of ϕX174 DNA synthesis (replicative form I, RFI) was irradiated in nitrogen-saturated aqueous solution. Under these conditions, OH· and e_aq⁻ are the main primary radicals and the yield of H· is approximately one-fifth of the other two species. The DNA was protected from radiation-induced strand breaks by the hydroxyl radical scavengers, potassium ferrocyanide and potassium iodide. Addition of potassium permanganate, which reacts with the electron and the hydrogen radical, afforded little protection. Potassium nitrate, which is an efficient electron radical scavenger, produced little protection against strand breaks. The hydroxyl radical is apparently the important species of water radiolysis involved in secondary radiation damage to DNA expressed as strand breaks. An important feature of this study was that the analysis for radiation damage was performed without exposure of the DNA to extensive chemical treatment or unknown cellular enzymes.