Effect of repeat instability on cancer and neurological diseases

在eulkaryotic细胞中，DNA聚合酶a（pol a）在复制起点和冈崎片段的5'端启动DNA合成。Pol - a缺乏纠正核苷酸错配错误的校对活性，但它不能有效地延伸错配的31端。这可能导致不匹配/不对齐的DNA引物过早终止。突变聚合酶L868F pol a比野生型pol a更频繁地催化核苷酸错误结合和错误延伸。我们已经证明由pol a产生的不匹配引物可以在需要PCNA的反应中被pol C延长，但不包括不匹配引物。携带pol A的L868F或L868M等位基因的酵母菌产生+1帧移的速率很高，而缺乏pol c催化亚基的菌株产生+1帧移的速率降低。突变依赖于PCNA Lys164，位于RAD18的下游。此外，pol S外切酶的失活增加了pol t依赖的+1帧移的比例。这些数据表明，PCNA和pol在一个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，pol a PCNA-和pol C依赖性DNA合成可能是驱动进化的遗传变异的来源，也可能是导致功能障碍和疾病的潜在突变的来源

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