Worth L, Clark S, Radman M, Modrich P
Department of Biochemistry, Duke University Medical Center, Durham, NC 27710.
Proc Natl Acad Sci U S A. 1994 Apr 12;91(8):3238-41. doi: 10.1073/pnas.91.8.3238.
Bacterial mutS and mutL mutations confer large increases in recombination between sequences that are divergent by several percent at the nucleotide level, an effect attributed to a role for products of these genes in control of recombination fidelity. Since MutS and MutL are proteins involved in the earliest steps of mismatch repair, including mismatch recognition by MutS, we have tested the possibility that they may affect strand exchange in response to occurrence of mispairs within the recombination heteroduplex. We show that MutS abolishes RecA-catalyzed strand transfer between fd and M13 bacteriophage DNAs, which vary by 3% at the nucleotide level, but is without effect on M13-M13 or fd-fd exchange. Although MutL alone has no effect on M13-fd heteroduplex formation, the protein dramatically enhances the inhibition of strand transfer mediated by MutS. Analysis of strand-transfer intermediates that accumulate in the presence of MutS and MutL indicates that the proteins block branch migration, presumably in response to occurrence of mispairs within newly formed heteroduplex.
细菌mutS和mutL突变导致核苷酸水平上有百分之几差异的序列之间的重组大幅增加，这种效应归因于这些基因的产物在控制重组保真度方面的作用。由于MutS和MutL是参与错配修复最早步骤的蛋白质，包括MutS对错配的识别，我们测试了它们可能因重组异源双链体内错配的出现而影响链交换的可能性。我们发现，MutS消除了fd和M13噬菌体DNA之间由RecA催化的链转移，这两种噬菌体DNA在核苷酸水平上有3%的差异，但对M13-M13或fd-fd交换没有影响。虽然单独的MutL对M13-fd异源双链体的形成没有影响，但该蛋白质显著增强了由MutS介导的对链转移的抑制作用。对在MutS和MutL存在下积累的链转移中间体的分析表明，这些蛋白质阻止了分支迁移，推测是对新形成的异源双链体内错配的出现做出反应。
