Effect of repeat instability on cancer and neurological diseases

在真核细胞中，DNA聚合酶a(Pola)在复制起始处和Okazaki片段的5‘端启动DNA合成。POLA缺乏纠正核苷酸错配错误的校对活性，但它低效地延伸错配的31末端。这可能会导致不匹配/不对准的DNA引物提前终止。突变子聚合酶L868F pola比野生型pola更频繁地催化核苷酸错掺和错延伸。我们已经展示了错位的引物，但没有错配的引物，Pola产生的错配引物可以被polC在需要增殖细胞核抗原的反应中延伸。携带polA的L868F或L868M等位基因的酵母菌产生1移码的频率很高，而缺乏polC催化亚基的菌株的移码频率降低。突变依赖于增殖细胞核抗原Lys164，位于RAD18的下游。此外，POL S核酸外切酶失活后，依赖POL T的1号移码比例增加。这些数据表明，增殖细胞核抗原和POL在复制错误促进途径中合作，该途径可能针对错位错误。在这种情况下，Pola依赖于增殖细胞核抗原和PolC DNA合成可能是驱动进化的遗传变异的来源，或者是可能导致功能障碍和疾病的突变的来源

In eulcaryotic cells, DNA polymerase a(pol a)initiates DNA synthesis at replication origins and at the 5'-ends of Okazaki fragments. Pol a lacks proofreading activity for correcting nucleotide misincorporation errors, but it extends mismatched 31-termini inefficiently. This can lead to premature termination of mismatched/misaligned DNA primers. The mutator polymerase L868F pol a catalyzes nucleotide misincorporation and misextension more frequently than wild type pol a. We have shown misaligned primers, but not the mismatched primers, generated by pol a can be extended by pol C in a reaction that requires PCNA. A yeast strain carrying L868F or L868M allele of pol a generated +1 frameshifts at a high rate, and this rate was decreased in strains lacking the catalytic subunit of pol C. Mutations were dependent on PCNA Lys164, and were downstream of the RAD18. Furthermore, inactivation of pol S exonuclease increased the proportion of pol t -dependent +1 frameshifts. These data suggest that PCNA and pol t cooperate in a replication error promoting pathway that may be targeted to misalignment errors. In this context, pol a PCNA-, and pol C -dependent DNA synthesis may be a source of genetic variation which drives evolution or a source of mutations with potential to cause dysfunction and disease