Je K H, Son J K, O'Connor T R, Lee C S
Department of Biochemistry, College of Natural Sciences, Yeungnam University, Kyongsan, Korea.
Mol Cells. 1998 Dec 31;8(6):691-7.
A variety of alkylated base adducts are repaired by 3-methyladenine DNA glycosylases, one of the base excision repair enzymes. In this study, we examined the DNA adducts induced by hepsulfam and determined whether alkylated base adducts can be substrates for bacterial and mammalian 3-methyladenine DNA glycosylases by electrophoresis methods. Hepsulfam, a synthetic analogue of busulfan, is known to alkylate DNA and form interstrand cross-links. The extent of DNA interstrand cross-links induced by hepsulfam and busulfan was found to be similar but significantly lower than that induced by chlorambucil, as measured by an agarose gel assay. The major monofunctional alkylation site of hepsulfam was observed at the N7 position of guanine, and not at the N3 position of adenine. Both compounds did not exhibit any sequence selective DNA alkylation patterns. The excision of hepsulfam-induced DNA adducts has been determined by treatment with homogeneous recombinant bacterial, rat and human 3-methyladenine DNA glycosylases and successive treatments by formamidopyrimidine-DNA glycosylase. The Escherichia coli alkA protein was shown to completely excise N7 guanine adducts, whereas mammalian 3-methyladenine DNA glycosylase failed to excise them. In addition, the cytotoxicity assay showed that E. coli mutant strains defective in the alkA gene or the uvrA gene were more sensitive to killing by hepsulfam than the wild type.
多种烷基化碱基加合物可被3-甲基腺嘌呤DNA糖基化酶修复，3-甲基腺嘌呤DNA糖基化酶是碱基切除修复酶之一。在本研究中，我们检测了庚磺烷诱导的DNA加合物，并通过电泳方法确定烷基化碱基加合物是否可作为细菌和哺乳动物3-甲基腺嘌呤DNA糖基化酶的底物。庚磺烷是白消安的合成类似物，已知其可使DNA烷基化并形成链间交联。通过琼脂糖凝胶试验测定，发现庚磺烷和白消安诱导的DNA链间交联程度相似，但明显低于苯丁酸氮芥诱导的程度。观察到庚磺烷的主要单功能烷基化位点在鸟嘌呤的N7位置，而非腺嘌呤的N3位置。这两种化合物均未表现出任何序列选择性DNA烷基化模式。通过用同源重组细菌、大鼠和人类3-甲基腺嘌呤DNA糖基化酶处理以及随后用甲酰胺嘧啶-DNA糖基化酶处理，已确定了庚磺烷诱导的DNA加合物的切除情况。大肠杆菌alkA蛋白可完全切除N7鸟嘌呤加合物，而哺乳动物3-甲基腺嘌呤DNA糖基化酶则无法切除。此外，细胞毒性试验表明，alkA基因或uvrA基因缺陷的大肠杆菌突变菌株比野生型对庚磺烷杀伤更敏感。
