Zuo S, Boorstein R J, Teebor G W
Department of Biology, New York University Graduate School of Arts and Sciences, New York 10003, USA.
Nucleic Acids Res. 1995 Aug 25;23(16):3239-43. doi: 10.1093/nar/23.16.3239.
Exposure of pyrimidines of DNA to ionizing radiation under aerobic conditions or oxidizing agents results in attack on the 5,6 double bond of the pyrimidine ring or on the exocyclic 5-methyl group. The primary product of oxidation of the 5,6 double bond of thymine is thymine glycol, while oxidation of the 5-methyl group yields 5-hydroxymethyluracil. Oxidation of the 5,6 double bond of cytosine yields cytosine glycol, which decomposes to 5-hydroxycytosine, 5-hydroxyuracil and uracil glycol, all of which are repaired in DNA by Escherichia coli endonuclease III. We now describe the products of oxidation of 5-methylcytosine in DNA. Poly(dG-[3H]dmC) was gamma-irradiated or oxidized with hydrogen peroxide in the presence of Fe3+ and ascorbic acid. The oxidized co-polymer was incubated with endonuclease III or 5-hydroxymethyluracil-DNA glycosylase, to determine whether repairable products were formed, or digested to 2'-deoxyribonucleosides, to determine the total complement of oxidative products. Oxidative attack on 5-methylcytosine resulted primarily in formation of thymine glycol. The radiogenic yield of thymine glycol in poly(dG-dmC) was the same as that in poly(dA-dT), demonstrating that 5-methylcytosine residues in DNA were equally susceptible to radiation-induced oxidation as were thymine residues.
在有氧条件下或接触氧化剂时，DNA中的嘧啶暴露于电离辐射会导致嘧啶环的5,6双键或环外5-甲基受到攻击。胸腺嘧啶5,6双键氧化的主要产物是胸腺嘧啶二醇，而5-甲基氧化则产生5-羟甲基尿嘧啶。胞嘧啶5,6双键氧化产生胞嘧啶二醇，其分解为5-羟基胞嘧啶、5-羟基尿嘧啶和尿嘧啶二醇，所有这些在DNA中均可被大肠杆菌内切酶III修复。我们现在描述DNA中5-甲基胞嘧啶的氧化产物。聚（dG-[3H]dmC）在Fe3+和抗坏血酸存在下进行γ射线辐照或用过氧化氢氧化。将氧化后的共聚物与内切酶III或5-羟甲基尿嘧啶-DNA糖基化酶一起孵育，以确定是否形成可修复产物，或将其消化为2'-脱氧核糖核苷，以确定氧化产物的总组成。对5-甲基胞嘧啶的氧化攻击主要导致胸腺嘧啶二醇的形成。聚（dG-dmC）中胸腺嘧啶二醇的辐射产率与聚（dA-dT）中的相同，表明DNA中的5-甲基胞嘧啶残基与胸腺嘧啶残基一样，同样易受辐射诱导的氧化作用。
