Bogden J M, Eastman A, Bresnick E
Nucleic Acids Res. 1981 Jul 10;9(13):3089-103. doi: 10.1093/nar/9.13.3089.
An activity from mouse liver with catalyzes the disappearance of O6-methylguanine from DNA methylated with methylnitrosourea has been partially purified by ammonium sulfate fractionation and DNA-cellulose chromatography. The activity does not require divalent metal ions and is not affected by EDTA. It is specific for the repair of O6-methylguanine lesions and does not affect the removal of 7-methylguanine, 7-methyladenine or 3-methyladenine. The disappearance of O6-methylguanine is linear with respect to the concentration of protein and is dependent on incubation temperature. The kinetics and substrate dependence experiments suggest that the protein factor is product-inactivated. Amino acid analysis of hydrolysates of protein obtained after incubation of methylated DNA with the protein factor indicates the presence of radiolabeled S-methyl-L-cysteine, suggesting that during the repair of O6-methylguanine from methylated DNA, the methyl group is transferred to a sulfhydryl of a cysteine residue of a protein. This represents the first such demonstration in a mammalian system.
一种来自小鼠肝脏的活性物质，它能催化经甲基亚硝基脲甲基化的DNA中O6-甲基鸟嘌呤的消失，该活性物质已通过硫酸铵分级分离和DNA纤维素色谱法进行了部分纯化。该活性不需要二价金属离子，且不受EDTA影响。它对O6-甲基鸟嘌呤损伤的修复具有特异性，不影响7-甲基鸟嘌呤、7-甲基腺嘌呤或3-甲基腺嘌呤的去除。O6-甲基鸟嘌呤的消失与蛋白质浓度呈线性关系，且依赖于孵育温度。动力学和底物依赖性实验表明该蛋白质因子被产物失活。用甲基化DNA与蛋白质因子孵育后得到的蛋白质水解产物的氨基酸分析表明存在放射性标记的S-甲基-L-半胱氨酸，这表明在从甲基化DNA修复O6-甲基鸟嘌呤的过程中，甲基基团转移到了蛋白质半胱氨酸残基的巯基上。这是在哺乳动物系统中的首次此类证明。
