Gu L, Hong Y, McCulloch S, Watanabe H, Li G M
Department of Pathology and Laboratory Medicine, Lucille P.Markey Cancer Center, Graduate Center for Toxicology, University of Kentucky, Lexington, KY 40536, USA.
Nucleic Acids Res. 1998 Mar 1;26(5):1173-8. doi: 10.1093/nar/26.5.1173.
DNA mismatch repair ensures genomic stability by correcting biosynthetic errors and by blocking homologous recombination. MutS-like and MutL-like proteins play important roles in these processes. In Escherichia coli and yeast these two types of proteins form a repair initiation complex that binds to mismatched DNA. However, whether human MutS and MutL homologs interact to form a complex has not been elucidated. Using immunoprecipitation and Western blot analysis we show here that human MSH2, MLH1, PMS2 and proliferating cell nuclear antigen (PCNA) can be co-immunoprecipitated, suggesting formation of a repair initiation complex among these proteins. Formation of the initiation complex is dependent on ATP hydrolysis and at least functional MSH2 and MLH1 proteins, because the complex could not be detected in tumor cells that produce truncated MLH1 or MSH2 protein. We also demonstrate that PCNA is required in human mismatch repair not only at the step of repair initiation, but also at the step of repair DNA re-synthesis.
DNA错配修复通过纠正生物合成错误和阻断同源重组来确保基因组稳定性。MutS样蛋白和MutL样蛋白在这些过程中发挥着重要作用。在大肠杆菌和酵母中，这两类蛋白形成一个与错配DNA结合的修复起始复合物。然而，人类MutS和MutL同源物是否相互作用形成复合物尚未阐明。我们在此通过免疫沉淀和蛋白质印迹分析表明，人类MSH2、MLH1、PMS2和增殖细胞核抗原（PCNA）可以被共免疫沉淀，这表明这些蛋白之间形成了一个修复起始复合物。起始复合物的形成依赖于ATP水解以及至少功能性的MSH2和MLH1蛋白，因为在产生截短的MLH1或MSH2蛋白的肿瘤细胞中无法检测到该复合物。我们还证明，PCNA在人类错配修复中不仅在修复起始步骤是必需的，而且在修复DNA重新合成步骤也是必需的。
