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Role of DNA Polymerase η in the Bypass of a (6-4) TT Photoproduct

机译：DNA聚合酶η在（6-4）TT光产物旁路中的作用

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UV light-induced DNA lesions block the normal replication machinery. Eukaryotic cells possess DNA polymerase η (Polη), which has the ability to replicate past a cis-syn thymine-thymine (TT) dimer efficiently and accurately, and mutations in human Polη result in the cancer-prone syndrome, the variant form of xeroderma pigmentosum. Here, we test Polη for its ability to bypass a (6-4) TT lesion which distorts the DNA helix to a much greater extent than acis-syn TT dimer. Opposite the 3′ T of a (6-4) TT photoproduct, both yeast and human Polη preferentially insert a G residue, but they are unable to extend from the inserted nucleotide. DNA Polζ, essential for UV induced mutagenesis, efficiently extends from the G residue inserted opposite the 3′ T of the (6-4) TT lesion by Polη, and Polζ inserts the correct nucleotide A opposite the 5′ T of the lesion. Thus, the efficient bypass of the (6-4) TT photoproduct is achieved by the combined action of Polη and Polζ, wherein Polη inserts a nucleotide opposite the 3′ T of the lesion and Polζ extends from it. These biochemical observations are in concert with genetic studies in yeast indicating that mutations occur predominantly at the 3′ T of the (6-4) TT photoproduct and that these mutations frequently exhibit a 3′ T→C change that would result from the insertion of a G opposite the 3′ T of the (6-4) TT lesion.
机译：紫外线诱导的DNA损伤会阻止正常的复制机制。真核细胞具有DNA聚合酶η（Polη），该酶具有有效且准确地复制通过顺式-syn 胸腺嘧啶-胸腺嘧啶（TT）二聚体的能力，而人类Polη的突变会导致癌症易发症候群，色素干皮的变体形式。在这里，我们测试Polη绕过（6-4）TT损伤的能力，该损伤使DNA螺旋变形的程度比顺式-顺式 TT二聚体更大。与（6-4）TT光产物的3'T相对，酵母和人Polη均优先插入G残基，但它们无法从插入的核苷酸延伸。 UV诱变所必需的DNAPolζ有效地从与（6-4）TT病变的3'T相对的G残基延伸至Polη，而Polζ则插入了与病变的5'T相对的正确核苷酸A。因此，通过Polη和Polζ的组合作用实现了（6-4）TT光产物的有效旁路，其中Polη插入了与病变的3'T相对的核苷酸，并且Polζ从其延伸。这些生化观察与酵母中的遗传研究一致，表明突变主要发生在（6-4）TT光产物的3'T处，并且这些突变通常表现出3'T→C的变化，这是由于插入了与（6-4）TT病变的3'T相对的G。

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