Smith C A, Okumoto D S
Biochemistry. 1984 Mar 27;23(7):1383-91. doi: 10.1021/bi00302a008.
Arabinocytidine and aphidicolin are inhibitors of alpha-DNA polymerase that have been shown to affect both normal DNA replication and repair synthesis in mammalian cells. In contradiction to the prevalent hypothesis that these inhibitors merely slow the polymerization rate at incision sites near lesions, our results suggest that the repair synthesis resistant to inhibitors is mediated by a separate pathway. Repair synthesis in contact-inhibited human cells following UV irradiation was inhibited 75-80% by arabinocytidine or aphidicolin, and most of the repair patches were not ligated into parental DNA, as judged by an enzymatic assay. However, the patches were not demonstrably shorter than those in untreated cells. Even following low-UV doses at which no inhibition of repair synthesis by the inhibitors was observed, a majority of the patches were not ligated. DNA polymerase beta is implicated in this alternate pathway, both by the known specificity of the inhibitors and by evidence from their sensitivity to S1 nuclease that the patches arise from displacement synthesis. The unligated patches are not degraded in vivo and eventually become ligated into parental DNA, very slowly in the presence of inhibitors but much more rapidly following their removal. Thus, under conditions of alpha-polymerase inhibition, a limited number of normal length repair patches are made, apparently by displacement synthesis, leaving displaced strands that remain substantially undegraded.
阿糖胞苷和阿非迪可林是α-DNA聚合酶的抑制剂，已证明它们会影响哺乳动物细胞中的正常DNA复制和修复合成。与普遍认为这些抑制剂仅减慢损伤附近切口位点的聚合速率的假设相反，我们的结果表明，对抑制剂具有抗性的修复合成是由一条独立的途径介导的。经紫外线照射后，接触抑制的人细胞中的修复合成被阿糖胞苷或阿非迪可林抑制了75%-80%，并且根据酶促测定判断，大多数修复片段未连接到亲本DNA中。然而，这些片段并不明显短于未处理细胞中的片段。即使在低紫外线剂量下未观察到抑制剂对修复合成的抑制作用，大多数片段也未连接。DNA聚合酶β与这条替代途径有关，这既基于抑制剂已知的特异性，也基于它们对S1核酸酶敏感性的证据，即这些片段是由置换合成产生的。未连接的片段在体内不会降解，最终会连接到亲本DNA中，在存在抑制剂的情况下连接非常缓慢，但在去除抑制剂后连接速度会快得多。因此，在α-聚合酶抑制的条件下，显然通过置换合成产生了数量有限的正常长度的修复片段，留下了基本上未降解的被置换链。
