Thymine fragment damage retained in the DNA polynucleotide chain after gamma irradiation in aerated solutions. II

The chemical modifications of the thymine fragment due to gamma irradiation of aerated solutions of DNA, which remain linked to the polynucleotide chain, were determined by hydrolysis. The formic acid hydrolysis was carried out at 900C and in this way cis- and trans-5,6-dihydroxy-5,6-dihydrothymine (1 and 2), 5-hydroxy-5-methylhydantoin (3), formylurea (4), and urea (5) were released from the DNA chain backbone by rupture of the N-glycosidic bond. These defects were characterized unambiguously by chromatography and microreactions. These hydrolysis conditions made it possible to measure the quantities of the main defects 1,2, (sum) and 3 which were borne by the polynucleotide chain. By taking advantage of the fact that carbonic oxide and pyruvamide were released directly from the chain during the irradiation the formation of the N-formamidodeoxyribose DNA defect (6) was demonstrated. A mechanism to explain the formation of these defects, 1 to 5 and 6, pyruvamide and carbonic oxide, is suggested