Tishkoff D X, Rockmill B, Roeder G S, Kolodner R D
Dana-Farber Cancer Institute, Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Genetics. 1995 Feb;139(2):495-509. doi: 10.1093/genetics/139.2.495.
Strand exchange protein 1 (Sep1) from Saccharomyces cerevisiae promotes homologous pairing of DNA in vitro and sep1 mutants display pleiotropic phenotypes in both vegetative and meiotic cells. In this study, we examined in detail the ability of the sep1 mutant to progress through meiosis I prophase and to undergo meiotic recombination. In meiotic return-to-growth experiments, commitment to meiotic recombination began at the same time in wild type and mutant; however, recombinants accumulated at decreased rates in the mutant. Gene conversion eventually reached nearly wild-type levels, whereas crossing over reached 15-50% of wild type. In an assay of intrachromosomal pop-out recombination, the sep1, dmc1 and rad51 single mutations had only small effects; however, pop-out recombination was virtually eliminated in the sep1 dmc1 and sep1 rad51 double mutants, providing evidence for multiple recombination pathways. Analysis of meiotic recombination intermediates indicates that the sep1 mutant is deficient in meiotic double-strand break repair. In a physical assay, the formation of mature reciprocal recombinants in the sep1 mutant was delayed relative to wild type and ultimately reached only 50% of the wild-type level. Electron microscopic analysis of meiotic nuclear spreads indicates that the sep1 delta mutant arrests in pachytene, with apparently normal synaptonemal complex. This arrest is RAD9-independent. We hypothesize that the Sep1 protein participates directly in meiotic recombination and that other strand exchange enzymes, acting in parallel recombination pathways, are able to substitute partially for the absence of the Sep1 protein.
酿酒酵母中的链交换蛋白1（Sep1）在体外促进DNA的同源配对，并且sep1突变体在营养细胞和减数分裂细胞中均表现出多效性表型。在本研究中，我们详细研究了sep1突变体在减数分裂I前期进展以及进行减数分裂重组的能力。在减数分裂恢复生长实验中，野生型和突变体中减数分裂重组的起始时间相同；然而，突变体中重组体的积累速率降低。基因转换最终达到接近野生型的水平，而交叉互换达到野生型的15 - 50%。在染色体内部弹出重组的检测中，sep1、dmc1和rad51单突变只有很小的影响；然而，sep1 dmc1和sep1 rad51双突变体中弹出重组几乎完全消除，这为多种重组途径提供了证据。减数分裂重组中间体的分析表明，sep1突变体在减数分裂双链断裂修复方面存在缺陷所提供了证据。在一项物理检测中，sep1突变体中成熟的相互重组体的形成相对于野生型延迟，最终仅达到野生型水平的50%。减数分裂核铺展的电子显微镜分析表明，sep1Δ突变体在粗线期停滞，联会复合体明显正常。这种停滞不依赖于RAD9。我们推测Sep1蛋白直接参与减数分裂重组，并且其他在平行重组途径中起作用的链交换酶能够部分替代Sep1蛋白的缺失。
