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In situ Enzymatic Reclosure of Opened Imidazole Rings of Purines in DNA Damaged by γ -irradiation

Christopher J. Chetsanga and Cheryl Grigorian
Proceedings of the National Academy of Sciences of the United States of America
Vol. 82, No. 3 (Feb. 1, 1985), pp. 633-637
Stable URL: http://www.jstor.org/stable/25324
Page Count: 5
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In situ Enzymatic Reclosure of Opened Imidazole Rings of Purines in DNA Damaged by γ -irradiation
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Abstract

When aqueous solutions of DNA were treated with 10-500 grays of γ -rays, the imidazole rings of some adenine and guanine residues underwent scission, resulting in the conversion of these purines to formamidopyrimidines. It was found that formamidopyrimidine-DNA glycosylase, known to remove imidazole-ring-opened 7-methylguanine from DNA, did not excise the radiation-induced non-alkylated formamidopyrimidines formed from adenine and guanine. The repair of these ring-opened purines was found to involve an enzymatic recyclizing of the opened imidazole ring that effects a restoration of the C-8 to N-9 bond. The enzyme, purine imidazole-ring cyclase reclosed the imidazole rings of 90% of ring-opened adenine or guanine, but did not close the opened imidazole ring of 7-methylguanine-derived formamidopyrimidine in DNA.

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