Laboratory of Molecular Genetics and Laboratory of Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC 27709, USA.
Proc Natl Acad Sci U S A. 2010 Dec 7;107(49):21070-5. doi: 10.1073/pnas.1013048107. Epub 2010 Nov 1.
Mismatch repair (MMR) of replication errors requires DNA ends that can direct repair to the newly synthesized strand containing the error. For all but those organisms that use adenine methylation to generate nicks, the source of these ends in vivo is unknown. One possibility is that MMR may have a "special relation to the replication complex" [Wagner R, Jr., Meselson M (1976) Proc Natl Acad Sci USA 73:4135-4139], perhaps one that allows 5' or 3' DNA ends associated with replication to act as strand discrimination signals. Here we examine this hypothesis, based on the logic that errors made by yeast DNA polymerase α (Pol α), which initiates Okazaki fragments during lagging-strand replication, will always be closer to a 5' end than will be more internal errors generated by DNA polymerase δ (Pol δ), which takes over for Pol α to complete lagging-strand replication. When we compared MMR efficiency for errors made by variant forms of these two polymerases, Msh2-dependent repair efficiencies for mismatches made by Pol α were consistently higher than for those same mismatches when made by Pol δ. Thus, one special relationship between MMR and replication is that MMR is more efficient for the least accurate of the major replicative polymerases, exonuclease-deficient Pol α. This observation is consistent with the close proximity and possible use of 5' ends of Okazaki fragments for strand discrimination, which could increase the probability of Msh2-dependent MMR by 5' excision, by a Msh2-dependent strand displacement mechanism, or both.
错配修复（MMR）需要复制错误的 DNA 末端，这些末端可以将修复导向包含错误的新合成链。对于除了那些使用腺嘌呤甲基化生成切口的生物体之外，这些末端在体内的来源尚不清楚。一种可能性是 MMR 可能与“复制复合物有特殊关系”[Wagner R，Jr.，Meselson M（1976）Proc Natl Acad Sci USA 73：4135-4139]，也许它允许与复制相关的 5' 或 3' DNA 末端充当链区分信号。在这里，我们根据酵母 DNA 聚合酶 α（Pol α）在滞后链复制期间引发 Okazaki 片段的错误总是比由 DNA 聚合酶 δ（Pol δ）生成的更内部错误更接近 5' 端的逻辑来检验这一假设，Pol δ 接替 Pol α 完成滞后链复制。当我们比较这两种聚合酶变体产生的错误的 MMR 效率时，Msh2 依赖性修复效率对于由 Pol α 产生的错配始终高于由 Pol δ 产生的相同错配。因此，MMR 和复制之间的一种特殊关系是，对于主要复制聚合酶中最不准确的 Pol α 缺乏外切酶，MMR 的效率更高。这一观察结果与 Okazaki 片段的 5' 末端的接近度和可能的使用一致，这可以通过 5' 切除、Msh2 依赖性链置换机制或两者的结合来增加 Msh2 依赖性 MMR 的概率。
