Dynamics of Homology Searching During Gene Conversion in Saccharomyces cerevisiae Revealed by Donor Competition
Dynamics of Homology Searching During Gene Conversion in Saccharomyces cerevisiae Revealed by Donor Competition
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DOI：
10.1534/genetics.111.132738
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发表时间：
2011-12-01
期刊：
影响因子：
3.3
通讯作者：
Haber, James E.
中科院分区：
文献类型：
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作者：
Coic, Eric;Martin, Joshua;Haber, James E.
同源重组最不为人所知的一个方面是双链断裂（DSB）的末端在整个基因组中搜索可用于修复断裂的同源模板的过程。我们利用了在HO核酸内切酶诱导的芽殖酵母MAT基因座转换过程中使用的替代供体HML和HMR之间的自然竞争。强交配型依赖性的偏见在选择的捐助者是强制执行的重组增强子（RE），它位于17 kb接近HML。我们调查了改善不利供体使用的因素。我们表明，正常的异染色质状态的捐助者不损害捐助者的使用，因为捐助者的选择是不受影响，消除这种表观遗传沉默。相比之下，增加不利供体共享的同源性的长度增加了其使用。该结果表明，供体选择不是不可撤销的，并且意味着在重组完成之前，DSB末端甚至有利的供体之间存在多次相遇。通过添加更多的同源性的增加不是线性的;这些结果可以通过热力学模型来解释，该模型确定了使用一种供体的能量成本。从这个分析的一个重要推论是，当HML作为供体时，RE导致其与MAT的有效基因组距离从200 kb减少到接近20 kb，我们假设这发生在DSB创建后，通过MAT周围的表观遗传染色质修饰。
One of the least understood aspects of homologous recombination is the process by which the ends of a double-strand break (DSB) search the entire genome for homologous templates that can be used to repair the break. We took advantage of the natural competition between the alternative donors HML and HMR employed during HO endonuclease-induced switching of the budding yeast MAT locus. The strong mating-type-dependent bias in the choice of the donors is enforced by the recombination enhancer (RE), which lies 17 kb proximal to HML. We investigated factors that improve the use of the disfavored donor. We show that the normal heterochromatic state of the donors does not impair donor usage, as donor choice is not affected by removing this epigenetic silencing. In contrast, increasing the length of homology shared by the disfavored donor increases its use. This result shows that donor choice is not irrevocable and implies that there are several encounters between the DSB ends and even the favored donor before recombination is accomplished. The increase by adding more homology is not linear; these results can be explained by a thermodynamic model that determines the energy cost of using one donor over the other. An important inference from this analysis is that when HML is favored as the donor, RE causes a reduction in its effective genomic distance from MAT from 200 kb to similar to 20 kb, which we hypothesize occurs after the DSB is created, by epigenetic chromatin modifications around MAT.