DNA double-strand breaks (DSBs) constitute one of the most cytotoxic forms of DNA damage and pose a significant threat to cell viability, survival, and homeostasis. DSBs have the potential to promote aneuploidy, cell death and potentially deleterious mutations that promote tumorigenesis. Homologous recombination (HR) is one of the main DSB repair pathways and while being essential for cell survival under genotoxic stress, it requires proper regulation to avoid chromosome rearrangements. Here, we characterize the Saccharomyces cerevisiae E3 ubiquitin ligase/putative helicase Irc20 as a regulator of HR. Using purified Irc20, we show that it can hydrolyze ATP in the presence and absence of DNA, but does not increase access to DNA within a nucleosome. In addition, we show that both the ATPase and ubiquitin ligase activities of Irc20 are required for suppressing the spontaneous formation of recombination foci. Finally, we demonstrate a role for Irc20 in promoting Rad51 chromatin association and the removal of Rad52 recombinase from chromatin, thus facilitating subsequent HR steps and directing recombination to more error-free modes.

DNA 双链断裂 (DSB) 是最具细胞毒性的 DNA 损伤形式之一，对细胞活力、存活和体内平衡构成重大威胁。DSBs 有可能促进非整倍性、细胞死亡和促进肿瘤发生的潜在有害突变。同源重组 (HR) 是主要的 DSB 修复途径之一，虽然对基因毒性应激下的细胞存活至关重要，但它需要适当的调节以避免染色体重排。在这里，我们描述了酿酒酵母E3 泛素连接酶/推定的解旋酶 Irc20 作为 HR 的调节剂。使用纯化的 Irc20，我们表明它可以在存在和不存在 DNA 的情况下水解 ATP，但不会增加对核小体内 DNA 的访问。此外，我们表明 Irc20 的 ATP 酶和泛素连接酶活性都是抑制重组病灶自发形成所必需的。最后，我们证明了 Irc20 在促进 Rad51 染色质结合和从染色质中去除 Rad52 重组酶方面的作用，从而促进后续的 HR 步骤并将重组引导至更无错误的模式。