Colaiácovo M P, Pâques F, Haber J E
Rosenstiel Center and Department of Biology, Brandeis University, Waltham, Massachusetts 02454-9110, USA.
Genetics. 1999 Apr;151(4):1409-23. doi: 10.1093/genetics/151.4.1409.
Repair of a double-strand break (DSB) by homologous recombination depends on the invasion of a 3'-ended strand into an intact template sequence to initiate new DNA synthesis. When the end of the invading DNA is not homologous to the donor, the nonhomologous sequences must be removed before new synthesis can begin. In Saccharomyces cerevisiae, the removal of these ends depends on both the nucleotide excision repair endonuclease Rad1p/Rad10p and the mismatch repair proteins Msh2p/Msh3p. In rad1 or msh2 mutants, when both ends of the DSB have nonhomologous ends, repair is reduced approximately 90-fold compared to a plasmid with perfect ends; however, with only one nonhomologous end, repair is reduced on average only 5-fold. These results suggest that yeast has an alternative, but less efficient, way to remove a nonhomologous tail from the second end participating in gene conversion. When the removal of one nonhomologous end is impaired in rad1 and msh2 mutants, there is also a 1-hr delay in the appearance of crossover products of gene conversion, compared to noncrossovers. We interpret these results in terms of the formation and resolution of alternative intermediates of a synthesis-dependent strand annealing mechanism.
通过同源重组修复双链断裂（DSB）取决于一个3'端链侵入完整的模板序列以启动新的DNA合成。当侵入DNA的末端与供体不同源时，在新合成开始之前必须去除非同源序列。在酿酒酵母中，这些末端的去除取决于核苷酸切除修复内切酶Rad1p/Rad10p和错配修复蛋白Msh2p/Msh3p。在rad1或msh2突变体中，当DSB的两端都有非同源末端时，与具有完美末端的质粒相比，修复减少了约90倍；然而，只有一个非同源末端时，修复平均仅减少5倍。这些结果表明，酵母有一种替代的、但效率较低的方法来从参与基因转换的第二个末端去除非同源尾巴。当rad1和msh2突变体中一个非同源末端的去除受损时，与非交叉产物相比，基因转换交叉产物的出现也会延迟1小时。我们根据合成依赖链退火机制的替代中间体的形成和解决来解释这些结果。
