Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
Mol Cell Biol. 2010 Apr;30(8):1887-97. doi: 10.1128/MCB.01553-09. Epub 2010 Feb 12.
Double-strand breaks (DSBs) are particularly deleterious DNA lesions for which cells have developed multiple mechanisms of repair. One major mechanism of DSB repair in mammalian cells is homologous recombination (HR), whereby a homologous donor sequence is used as a template for repair. For this reason, HR repair of DSBs is also being exploited for gene modification in possible therapeutic approaches. HR is sensitive to sequence divergence, such that the cell has developed ways to suppress recombination between diverged ("homeologous") sequences. In this report, we have examined several aspects of HR between homeologous sequences in mouse and human cells. We found that gene conversion tracts are similar for mouse and human cells and are generally < or =100 bp, even in Msh2(-)(/)(-) cells which fail to suppress homeologous recombination. Gene conversion tracts are mostly unidirectional, with no observed mutations. Additionally, no alterations were observed in the donor sequences. While both mouse and human cells suppress homeologous recombination, the suppression is substantially less in the transformed human cells, despite similarities in the gene conversion tracts. BLM-deficient mouse and human cells suppress homeologous recombination to a similar extent as wild-type cells, unlike Sgs1-deficient Saccharomyces cerevisiae.
双链断裂（DSBs）是对细胞具有多种修复机制的特别有害的 DNA 损伤。哺乳动物细胞中 DSB 修复的主要机制之一是同源重组（HR），其中同源供体序列用作修复模板。因此，HR 修复 DSB 也被用于可能的治疗方法中的基因修饰。HR 对序列差异很敏感，因此细胞已经开发出抑制差异（“同源”）序列之间重组的方法。在本报告中，我们研究了小鼠和人细胞中同源序列之间 HR 的几个方面。我们发现，即使在未能抑制同源重组的 Msh2(-)(/)(-)细胞中，基因转换片段也相似，并且通常 <或=100bp。基因转换片段主要是单向的，没有观察到突变。此外，在供体序列中没有观察到任何改变。虽然小鼠和人细胞都抑制同源重组，但转化的人细胞中的抑制作用大大降低，尽管基因转换片段相似。BLM 缺陷型小鼠和人类细胞对同源重组的抑制程度与野生型细胞相似，而不像 Sgs1 缺陷型酿酒酵母。
