Department of Chromosome Biology, Max F. Perutz Laboratories, Center for Molecular Biology, University of Vienna, A-1030 Vienna, Austria.
Nucleic Acids Res. 2013 Nov;41(20):9296-309. doi: 10.1093/nar/gkt703. Epub 2013 Aug 9.
Mus81 resolvase and Sgs1 helicase have well-established roles in mitotic DNA repair. Moreover, Mus81 is part of a minor crossover (CO) pathway in the meiosis of budding yeast, plants and vertebrates. The major pathway depends on meiosis-specific synaptonemal complex (SC) formation, ZMM proteins and the MutLγ complex for CO-directed resolution of joint molecule (JM)-recombination intermediates. Sgs1 has also been implicated in this pathway, although it may mainly promote the non-CO outcome of meiotic repair. We show in Tetrahymena, that homologous chromosomes fail to separate and JMs accumulate in the absence of Mus81 or Sgs1, whereas deletion of the MutLγ-component Mlh1 does not affect meiotic divisions. Thus, our results are consistent with Mus81 being part of an essential, if not the predominant, CO pathway in Tetrahymena. Sgs1 may exert functions similar to those in other eukaryotes. However, we propose an additional role in supporting homologous CO formation by promoting homologous over intersister interactions. Tetrahymena shares the predominance of the Mus81 CO pathway with the fission yeast. We propose that in these two organisms, which independently lost the SC during evolution, the basal set of mitotic repair proteins is sufficient for executing meiotic recombination.
Mus81 核酸酶和 Sgs1 解旋酶在有丝分裂 DNA 修复中起着重要作用。此外，Mus81 是芽殖酵母、植物和脊椎动物减数分裂中次要交叉（CO）途径的一部分。主要途径依赖于减数分裂特异性联会复合体（SC）的形成、ZMM 蛋白和 MutLγ 复合物，以指导 CO 定向解决联会分子（JM）-重组中间体。Sgs1 也与该途径有关，尽管它可能主要促进减数修复的非 CO 结果。我们在四膜虫中表明，在缺乏 Mus81 或 Sgs1 的情况下，同源染色体无法分离，JM 积累，而 MutLγ 组件 Mlh1 的缺失并不影响减数分裂。因此，我们的结果与 Mus81 是 Tetrahymena 中必需的 CO 途径的一部分（如果不是主要途径的话）一致。Sgs1 可能发挥类似于其他真核生物的功能。然而，我们提出了一个额外的作用，通过促进同源 CO 形成来支持同源对姐妹染色单体的相互作用。四膜虫与裂殖酵母共享 Mus81 CO 途径的优势。我们提出，在这两个在进化过程中独立失去 SC 的生物体中，基本的有丝分裂修复蛋白足以执行减数分裂重组。
