Fabre Francis, Chan Allan, Heyer Wolf-Dietrich, Gangloff Serge
Unité Mixte de Recherche 217, Centre National de la Recherche Scientifique-Commissariat à l'Energie Atomique. Département de Radiobiologie et Radiopathologie BP6, 92265 Fontenay-aux-Roses, France.
Proc Natl Acad Sci U S A. 2002 Dec 24;99(26):16887-92. doi: 10.1073/pnas.252652399. Epub 2002 Dec 10.
Toxic recombination events are detected in vegetative Saccharomyces cerevisiae cells through negative growth interactions between certain combinations of mutations. For example, mutations affecting both the Srs2 and Sgs1 helicases result in extremely poor growth, a phenotype suppressed by mutations in genes that govern early stages of recombination. Here, we identify a similar interaction involving double mutations affecting Sgs1 or Top3 and Mus81 or Mms4. We also find that the primary DNA structures that initiate these toxic recombination events cannot be double-strand breaks and thus are likely to be single-stranded DNA. We interpret our results in the context of the idea that replication stalling leaves single-stranded DNA, which can then be processed by two competing mechanisms: recombination and nonrecombination gap-filling. Functions involved in preventing toxic recombination would either avoid replicative defects or act on recombination intermediates. Our results suggest that Srs2 channels recombination intermediates back into the gap-filling route, whereas Sgs1Top3 and Mus81Mms4 are involved in recombination andor in replication to allow replication restart.
通过某些突变组合之间的负生长相互作用，可在营养型酿酒酵母细胞中检测到毒性重组事件。例如，影响Srs2和Sgs1解旋酶的突变会导致生长极差，而控制重组早期阶段的基因突变所产生的突变可抑制该表型。在此，我们鉴定出一种类似的相互作用，涉及影响Sgs1或Top3以及Mus81或Mms4的双突变。我们还发现，引发这些毒性重组事件的主要DNA结构不可能是双链断裂，因此很可能是单链DNA。我们在复制停滞会留下单链DNA这一观点的背景下解释我们的结果，然后单链DNA可通过两种相互竞争的机制进行处理：重组和非重组性缺口填补。参与预防毒性重组的功能要么避免复制缺陷，要么作用于重组中间体。我们的结果表明，Srs2将重组中间体引导回缺口填补途径，而Sgs1Top3和Mus81Mms4参与重组和/或复制以允许复制重新启动。
