Gamma Radiolysis of RNA: An ESR and Spin-Trapping Study

Abstract

It is well known that the radiolytic cleavage of water produces hydroxyl radicals (·OH), hydrogen atoms (·H) and hydrated electrons (e- aq). Although these species react rapidly with the individual nucleic acid bases,2-4 it is generally accepted that when nucleic acid (DNA, RNA) solutions are exposed to ionizing radiation, the principal reaction leading to nucleic acid damage is caused by ·OH. Besides direct formation, ·OH is formed from H2O2, also a product of the radiolysis of water, in the presence of trace amounts of divalent metal ions.5 The study reported here deals with the reaction of RNA with ·OH, produced in aqueous solutions by gamma radiolysis. Of concern are the processes that occur following this reaction. For instance, are the precursors to the nucleic acid damage localized at specific base sites or do they occur indiscriminately throughout the nucleic acid molecule? Recently Kuwabara et al.6 using HPLC, spin trapping and ESR identified the precursors of thymine damage in X-irradiated DNA solutions. For the present study, poly A, poly C, poly G and poly U were used as standards for RNA, and RNA was used as a model system for similar reactions that may occur in DNA. The nucleic acid free radical intermediates were detected and identified by ESR and spin trapping following hydrolysis of the spin-trapped nucleic acid molecules.