Riazuddin S, Athar A, Sohail A
Centre for Advanced Molecular Biology, University of the Punjab, Lahore, Pakistan.
Nucleic Acids Res. 1987 Nov 25;15(22):9471-86. doi: 10.1093/nar/15.22.9471.
Three peaks of methyltransferase activity specific for MNNG alkylated DNA have been identified from extracts of chemically adapted M. luteus. They are designated as TI to TIII in order to their elution from a Sephadex G-75 column. The first one of these peaks has been purified to homogeneity. TI, is an inducible, unusually salt resistant, heat labile protein which corrects O6-methylguanine in alkylated DNA by the transfer of the O6-alkyl group to a cysteine amino acid in the TI protein. There is a stoichiometric relationship between the loss of O6-methylguanine from the DNA and the production of S-methylcysteine. Partially purified TII & TIII proteins show specificity for O4-alkylthymine and methyl phosphotriesters respectively. The mode of repair by the isolated methyltransferases is similar yet there is no competition for substrate specificity. The apparent molecular weights of TI, TII & TIII proteins are 31Kd, 22Kd, and 13Kd respectively.
已从化学适应性藤黄微球菌提取物中鉴定出三种对MNNG烷基化DNA具有特异性的甲基转移酶活性峰。根据它们从Sephadex G - 75柱上的洗脱顺序，将它们命名为TI至TIII。这些峰中的第一个已纯化至同质。TI是一种可诱导的、异常耐盐、热不稳定的蛋白质，它通过将O6 - 烷基基团转移到TI蛋白中的半胱氨酸氨基酸上来校正烷基化DNA中的O6 - 甲基鸟嘌呤。DNA中O6 - 甲基鸟嘌呤的损失与S - 甲基半胱氨酸的产生之间存在化学计量关系。部分纯化的TII和TIII蛋白分别对O4 - 烷基胸腺嘧啶和甲基磷酸三酯具有特异性。分离出的甲基转移酶的修复模式相似，但在底物特异性方面没有竞争。TI、TII和TIII蛋白的表观分子量分别为31Kd、22Kd和13Kd。
