Displacement loops (D-loops) are intermediates formed during homologous recombination that play a pivotal role in the fidelity of repair. Rdh54 (a.k.a. Tid1), a Rad54 paralog in Saccharomyces cerevisiae, is well-known for its role with Dmc1 recombinase during meiotic recombination. Yet contrary to Dmc1, Rdh54 is also present in somatic cells where its function is less understood. While Rdh54 enhances the Rad51 DNA strand invasion activity in vitro, it is unclear how it interplays with Rad54-mediated invasions. Here, we show that Rdh54 inhibits D-loop formation by Rad51 and Rad54 in an ATPase-independent manner. Using a novel D-loop Mapping Assay, we further demonstrate that Rdh54 uniquely restricts the lengths of Rad54-mediated D-loops. The alterations in D-loop properties appear to be important for cell survival and mating-type switch in haploid yeast, whereas Rdh54 expression is suppressed in diploids. We propose that Rdh54 and Rad54 compete for potential binding sites within the Rad51 filament, where Rdh54 acts as a physical roadblock to Rad54″s translocation activity, limiting D-loop formation and D-loop length.

中文翻译：

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Rdh54 / Tid1抑制Rad51-Rad54介导的D环形成并限制D环长度

置换环（D环）是在同源重组过程中形成的中间体，在修复的忠实性中起着关键作用。Rdh54（aka Tid1）是酿酒酵母中的Rad54旁系同源物，因其与Dmc1重组酶在减数分裂重组过程中的作用而闻名。然而，与Dmc1相反，Rdh54也存在于体细胞中，但对其功能的了解较少。尽管Rdh54增强了Rad51 DNA链在体外的侵袭活性，尚不清楚它如何与Rad54介导的入侵相互作用。在这里，我们显示Rdh54以非依赖于ATPase的方式抑制Rad51和Rad54的D环形成。使用新颖的D环映射分析，我们进一步证明Rdh54独特地限制Rad54介导的D环的长度。D环性质的改变似乎对单倍体酵母中的细胞存活和交配型转换很重要，而Rdh54表达在二倍体中受到抑制。我们建议Rdh54和Rad54竞争Rad51细丝内的潜在结合位点，其中Rdh54充当Rad54易位活性的物理障碍，限制了D环的形成和D环的长度。