Free-radical Formation in Irradiated Deoxyribonucleic Acid

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Abstract
Electron-spin-resonance spectroscopy has been used to study free radical formation in irradiated DNA, DNA containing bromo-uracil, RNA, thymine, uracil and related compounds. Radical yields have been measured both at 77°k and room temperature. It was found that (a) the free radicals in DNA were not formed preferentially on the thymine residue, (b) the replacement of thymine by bromo-uracil in DNA increased the radical yield but the increase was insufficient to account for the observed increase in radiosensitivity in cells, and (c) that room temperature irradiation produced twice as many radicals in DNA as irradiation at 77°k which correlated well with the observed temperature effect in dry phage.