Fasching Clare L, Cejka Petr, Kowalczykowski Stephen C, Heyer Wolf-Dietrich
Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, CA 95616-8665, USA.
Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, CA 95616-8665, USA; Department of Molecular & Cellular Biology, University of California, Davis, Davis, CA 95616-8665, USA.
Mol Cell. 2015 Feb 19;57(4):595-606. doi: 10.1016/j.molcel.2015.01.022.
The displacement loop (D loop) is a DNA strand invasion product formed during homologous recombination. Disruption of nascent D loops prevents recombination, and during synthesis-dependent strand annealing (SDSA), disruption of D loops extended by DNA polymerase ensures a non-crossover outcome. The proteins implicated in D loop disruption are DNA motor proteins/helicases that act by moving DNA junctions. Here we report that D loops can also be disrupted by DNA topoisomerase 3 (Top3), and this disruption depends on Top3's catalytic activity. Yeast Top3 specifically disrupts D loops mediated by yeast Rad51/Rad54; protein-free D loops or D loop mediated by bacterial RecA protein or human RAD51/RAD54 resist dissolution. Also, the human Topoisomerase IIIa-RMI1-RMI2 complex is capable of dissolving D loops. Consistent with genetic data, we suggest that the extreme growth defect and hyper-recombination phenotype of Top3-deficient yeast cells is partially a result of unprocessed D loops.
置换环（D环）是同源重组过程中形成的一种DNA链入侵产物。新生D环的破坏会阻止重组，并且在依赖合成的链退火（SDSA）过程中，DNA聚合酶延伸的D环的破坏确保了非交叉结果。与D环破坏相关的蛋白质是通过移动DNA连接点起作用的DNA运动蛋白/解旋酶。在此我们报告，D环也可被DNA拓扑异构酶3（Top3）破坏，且这种破坏依赖于Top3的催化活性。酵母Top3特异性破坏由酵母Rad51/Rad54介导的D环；无蛋白的D环或由细菌RecA蛋白或人RAD51/RAD54介导的D环抵抗溶解。此外，人拓扑异构酶IIIa-RMI1-RMI2复合物能够溶解D环。与遗传数据一致，我们认为Top3缺陷型酵母细胞的极端生长缺陷和高重组表型部分是未加工的D环的结果。
