Jessop Lea, Lichten Michael
Laboratory of Biochemistry and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892-4260, USA.
Mol Cell. 2008 Aug 8;31(3):313-23. doi: 10.1016/j.molcel.2008.05.021.
Budding yeast lacking the Sgs1 helicase and the Mus81/Mms4 endonuclease are inviable, and indirect studies implicate homologous recombination gone awry as the cause of death. We show that mutants lacking both enzymes have profound defects in meiotic recombination intermediate metabolism and crossover (CO) formation. Recombination intermediates (joint molecules, JMs) accumulate in these cells, many with structures that are infrequent in wild-type cells. These JMs persist, preventing nuclear division. Using an inducible expression system, we restored Mus81 or Sgs1 to sgs1 mus81 cells at a time when JMs are forming. Mus81 expression did not prevent JM formation but did restore JM resolution, CO formation, and nuclear division. In contrast, Sgs1 expression reduced the extent of JM accumulation. These results indicate that Sgs1 and Mus81/Mms4 collaborate to direct meiotic recombination toward interhomolog interactions that promote proper chromosome segregation, and also indicate that Mus81/Mms4 promotes JM resolution in vivo.
缺乏Sgs1解旋酶和Mus81/Mms4核酸内切酶的出芽酵母无法存活，间接研究表明同源重组出错是导致死亡的原因。我们发现，同时缺乏这两种酶的突变体在减数分裂重组中间体代谢和交叉（CO）形成方面存在严重缺陷。重组中间体（联会分子，JMs）在这些细胞中积累，许多具有在野生型细胞中不常见的结构。这些JMs持续存在，阻止核分裂。使用诱导表达系统，我们在JMs形成时将Mus81或Sgs1恢复到sgs1 mus81细胞中。Mus81的表达并没有阻止JM的形成，但确实恢复了JM的分解、CO的形成和核分裂。相比之下，Sgs1的表达减少了JM积累的程度。这些结果表明，Sgs1和Mus81/Mms4协同作用，将减数分裂重组导向促进正确染色体分离的同源间相互作用，也表明Mus81/Mms4在体内促进JM的分解。
