Oh Steve D, Lao Jessica P, Taylor Andrew F, Smith Gerald R, Hunter Neil
Department of Microbiology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
Mol Cell. 2008 Aug 8;31(3):324-36. doi: 10.1016/j.molcel.2008.07.006.
Saccharomyces cerevisiae RecQ helicase, Sgs1, and XPF family endonuclease, Mus81-Mms4, are implicated in processing joint molecule (JM) recombination intermediates. We show that cells lacking either enzyme frequently experience chromosome segregation problems during meiosis and that when both enzymes are absent attempted segregation fails catastrophically. In all cases, segregation appears to be impeded by unresolved JMs. Analysis of the DNA events of recombination indicates that Sgs1 limits aberrant JM structures that result from secondary strand-invasion events and often require Mus81-Mms4 for their normal resolution. Aberrant JMs contain high levels of single Holliday junctions and include intersister JMs, multichromatid JMs comprising three and four chromatids, and newly identified recombinant JMs containing two chromatids, one of which has undergone crossing over. Despite persistent JMs in sgs1 mms4 double mutants, crossover and noncrossover products still form at high levels. We conclude that Sgs1 and Mus81-Mms4 collaborate to eliminate aberrant JMs, whereas as-yet-unidentified enzymes process normal JMs.
酿酒酵母RecQ解旋酶Sgs1和XPF家族核酸内切酶Mus81-Mms4参与处理联合分子（JM）重组中间体。我们发现，缺乏任何一种酶的细胞在减数分裂过程中经常会遇到染色体分离问题，而当两种酶都缺失时，尝试进行的分离会灾难性地失败。在所有情况下，分离似乎都受到未解决的JM的阻碍。对重组DNA事件的分析表明，Sgs1限制了由二次链侵入事件导致的异常JM结构，并且这些结构的正常解析通常需要Mus81-Mms4。异常JM含有高水平的单Holliday连接，包括姐妹间JM、由三条和四条染色单体组成的多染色单体JM，以及新鉴定的含有两条染色单体的重组JM，其中一条已经发生了交叉。尽管在sgs1 mms4双突变体中存在持续的JM，但交叉和非交叉产物仍以高水平形成。我们得出结论，Sgs1和Mus81-Mms4协同作用以消除异常JM，而尚未鉴定的酶处理正常JM。
