The base and nucleotide excision repair pathways (BER and NER, respectively) are two major mechanisms that remove DNA lesions formed by the reactions of genotoxic intermediates with cellular DNA. We have demonstrated earlier that the oxidatively generated guanine lesions spiroiminodihydantoin (Sp) and 5-guanidinohydantoin (Gh) are excised from double-stranded DNA by competing BER and NER in whole-cell extracts [Shafirovich, V., et al. (2016) J. Biol. Chem. 321, 5309–5319]. In this work we compared the NER and BER yields with single Gh or Sp lesions embedded at the same sites in covalently closed circular pUC19NN plasmid DNA (cccDNA) and in the same but linearized form (linDNA) of this plasmid. The kinetics of the Sp and Gh BER and NER incisions were monitored in HeLa cell extracts. The yield of NER products is ∼5 times greater in covalently closed circular DNA than in the linearized form, while the BER yield is smaller by ∼20–30% depending on the guanine lesion. Control BER experiments with 8-oxo-7,8-dihydroguanine (8-oxoG) show that the BER yield is increased by a factor of only 1.4 ± 0.2 in cccDNA relative to linDNA. These surprising differences in BER and NER activities are discussed in terms of the lack of termini in covalently closed circular DNA and the DNA lesion search dynamics of the NER DNA damage sensor XPC-RAD23B and the BER enzyme OGG1 that recognizes and excises 8-oxoG.

中文翻译：

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含有氧化产生的鸟嘌呤损伤的 DNA 质粒中的碱基和核苷酸切除修复途径

碱基和核苷酸切除修复途径（分别为 BER 和 NER）是去除由基因毒性中间体与细胞 DNA 反应形成的 DNA 损伤的两种主要机制。我们之前已经证明，氧化产生的鸟嘌呤损伤螺亚氨基二乙内酰脲 (Sp) 和 5-胍基乙内酰脲 (Gh) 通过全细胞提取物中的竞争性 BER 和 NER 从双链 DNA 中切除 [Shafirovich, V., et al. (2016) J. 生物学。化学。321, 5309–5319]。在这项工作中，我们比较了嵌入共价闭合环状 pUC19NN 质粒 DNA (cccDNA) 和该质粒的相同但线性形式 (linDNA) 中相同位点的单个 Gh 或 Sp 损伤的 NER 和 BER 产量。在 HeLa 细胞提取物中监测 Sp 和 Gh BER 和 NER 切口的动力学。NER 产物的产率在共价闭合环状 DNA 中比线性形式高 5 倍，而 BER 产率则小 20-30%，具体取决于鸟嘌呤损伤。使用 8-oxo-7,8-dihydroguanine (8-oxoG) 进行的对照 BER 实验表明，相对于 linDNA，cccDNA 的 BER 产量仅增加了 1.4 ± 0.2 倍。