Huang J C, Hsu D S, Kazantsev A, Sancar A
Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill 27599.
Proc Natl Acad Sci U S A. 1994 Dec 6;91(25):12213-7. doi: 10.1073/pnas.91.25.12213.
Nucleotide-excision repair is the repair system for removing bulky lesions from DNA. Humans deficient in this repair pathway suffer from xeroderma pigmentosum (XP), a disease characterized by photodermatoses, including skin cancers. At the cellular level, XP patients fail to remove cyclobutane pyrimidine dimers and pyrimidine(6-4)pyrimidone photoproducts induced by UV light, as well as other bulky DNA lesions caused by various genotoxic agents. XP cells are not particularly sensitive to ionizing radiation or to alkylating agents that cause mostly nonbulky DNA lesions. Therefore, it has generally been assumed that the human nucleotide-excision repair enzyme (excinuclease) is specific for bulky adducts. To determine the substrate range of human excinuclease we used the highly sensitive excision assay and tested bulky adducts, synthetic apurinic/apyrimidinic sites, N6-methyladenine, O6-methylguanine, and mismatches as potential substrates. We found that all of these "lesions" were removed by human excinuclease, although with vastly different efficiencies.
核苷酸切除修复是一种从DNA中去除大片段损伤的修复系统。缺乏这种修复途径的人类会患着色性干皮病（XP），这是一种以光皮肤病为特征的疾病，包括皮肤癌。在细胞水平上，XP患者无法去除紫外线诱导产生的环丁烷嘧啶二聚体和嘧啶（6-4）嘧啶酮光产物，以及由各种基因毒性剂引起的其他大片段DNA损伤。XP细胞对电离辐射或主要引起非大片段DNA损伤的烷化剂并不特别敏感。因此，人们普遍认为人类核苷酸切除修复酶（外切核酸酶）对大片段加合物具有特异性。为了确定人类外切核酸酶的底物范围，我们使用了高灵敏度切除试验，并测试了大片段加合物、合成的无嘌呤/无嘧啶位点、N6-甲基腺嘌呤、O6-甲基鸟嘌呤以及错配作为潜在底物。我们发现所有这些“损伤”都能被人类外切核酸酶去除，尽管效率差异很大。
