Substitutions in the exonuclease domain of DNA polymerase ϵ cause ultramutated human tumors. Yeast and mouse mimics of the most common variant, P286R, produce mutator effects far exceeding the effect of Polϵ exonuclease deficiency. Yeast Polϵ-P301R has increased DNA polymerase activity, which could underlie its high mutagenicity. We aimed to understand the impact of this increased activity on the strand-specific role of Polϵ in DNA replication and the action of extrinsic correction systems that remove Polϵ errors. Using mutagenesis reporters spanning a well-defined replicon, we show that both exonuclease-deficient Polϵ (Polϵ-exo⁻) and Polϵ-P301R generate mutations in a strictly strand-specific manner, yet Polϵ-P301R is at least ten times more mutagenic than Polϵ-exo⁻ at each location analyzed. Thus, the cancer variant remains a dedicated leading-strand polymerase with markedly low accuracy. We further show that P301R substitution is lethal in strains lacking Polδ proofreading or mismatch repair (MMR). Heterozygosity for pol2-P301R is compatible with either defect but causes strong synergistic increases in the mutation rate, indicating that Polϵ-P301R errors are corrected by Polδ proofreading and MMR. These data reveal the unexpected ease with which polymerase exchange occurs in vivo, allowing Polδ exonuclease to prevent catastrophic accumulation of Polϵ-P301R-generated errors on the leading strand.

中文翻译：

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错配修复和DNA聚合酶δ校正可防止表达癌症相关的DNA聚合酶ϵ变异体的细胞中前导链错误的灾难性积累。

DNA聚合酶the的核酸外切酶结构域中的取代引起超突变的人类肿瘤。最常见的变体P286R的酵母和小鼠模拟物产生的突变效应远远超过Pol exceeding核酸外切酶缺乏症的影响。酵母Polϵ-P301R具有增强的DNA聚合酶活性，这可能是其高致突变性的基础。我们旨在了解这种活动增加对Polϵ在DNA复制中的链特​​异性作用的影响以及消除Polϵ错误的外在校正系统的作用。使用诱变记者跨越定义良好的复制，我们表明，无论是外切酶缺陷Polε（Polε外型^- ）和Polε-P301R生成一个特定的链严格地突变，但Polε-P301R是至少十倍不止诱变Polε外型^-在每个位置进行分析。因此，癌症变体仍然是专用的前导链聚合酶，其准确性明显较低。我们进一步表明，在缺乏Polδ校对或错配修复（MMR）的菌株中，P301R替代具有致命性。pol2-P301R的杂合性可与任一缺陷兼容，但会引起突变率的强烈协同增加，这表明Polδ-P301R错误已通过Polδ校对和MMR得以纠正。这些数据揭示了在体内发生聚合酶交换的出乎意料的简便性，使Polδ核酸外切酶可以防止Polϵ-P301R产生的错误在前导链上的灾难性积累。