Galloway A M, Liuzzi M, Paterson M C
Department of Medicine, Cross Cancer Institute, Edmonton, Alberta, Canada.
J Biol Chem. 1994 Jan 14;269(2):974-80.
A new nuclease digestion assay was developed to elucidate the human excision-repair system operating on cyclobutyl pyrimidine dimers and (6-4) photoproducts. We analyzed lesions that accumulated in excised oligonucleotide fragments during incubation of UV-treated cultured fibroblasts. (6-4) photoproducts were removed intact, whereas excised cyclobutyl dimers often contained ruptured interpyrimidine phosphodiester bonds, raising the possibility that the intradimer backbone-cleavage reaction may help promote the bypass of unexcised dimers by the DNA replication or RNA transcription machinery. Cell strains representing eight different inherited forms of the cancer-prone skin disease xeroderma pigmentosum (XP) were generally found to exhibit characteristic abilities to excise the two classes of photolesions, ranging from total deficiency in groups A and G to normal proficiency in the variant. The capacity of any given XP group to act on one class of photoproducts in no way predicted its ability to act on the other. Finally, in those XP strains displaying significant levels of dimer removal, the ratio of intact-versus-modified dimers was normal, implying that rupture of the intradimer backbone linkage occurs independently of subsequent excision-repair reactions. Our data indicate that cyclobutyl dimers and (6-4) photoproducts are processed by distinct nucleotide-excision-repair pathways in human cells.
开发了一种新的核酸酶消化试验，以阐明作用于环丁基嘧啶二聚体和（6-4）光产物的人类切除修复系统。我们分析了紫外线处理的培养成纤维细胞孵育期间在切除的寡核苷酸片段中积累的损伤。（6-4）光产物被完整去除，而切除的环丁基二聚体通常含有嘧啶间磷酸二酯键断裂，这增加了二聚体内骨架切割反应可能有助于促进DNA复制或RNA转录机制绕过未切除二聚体的可能性。一般发现代表八种不同遗传形式的易患癌症皮肤病色素性干皮病（XP）的细胞株具有切除两类光损伤的特征能力，从A组和G组的完全缺陷到变异型的正常能力。任何给定的XP组作用于一类光产物的能力绝不能预测其作用于另一类光产物的能力。最后，在那些显示出显著水平二聚体去除的XP菌株中，完整与修饰二聚体的比例是正常的，这意味着二聚体内骨架连接的断裂独立于随后的切除修复反应发生。我们的数据表明，环丁基二聚体和（6-4）光产物在人类细胞中通过不同的核苷酸切除修复途径进行处理。
