The licensing step of DNA double-strand break repair by homologous recombination entails resection of DNA ends to generate a single-stranded DNA template for assembly of the repair machinery consisting of the RAD51 recombinase and ancillary factors¹. DNA end resection is mechanistically intricate and reliant on the tumour suppressor complex BRCA1–BARD1 (ref. ²). Specifically, three distinct nuclease entities—the 5′–3′ exonuclease EXO1 and heterodimeric complexes of the DNA endonuclease DNA2, with either the BLM or WRN helicase—act in synergy to execute the end resection process³. A major question concerns whether BRCA1–BARD1 directly regulates end resection. Here, using highly purified protein factors, we provide evidence that BRCA1–BARD1 physically interacts with EXO1, BLM and WRN. Importantly, with reconstituted biochemical systems and a single-molecule analytical tool, we show that BRCA1–BARD1 upregulates the activity of all three resection pathways. We also demonstrate that BRCA1 and BARD1 harbour stand-alone modules that contribute to the overall functionality of BRCA1–BARD1. Moreover, analysis of a BARD1 mutant impaired in DNA binding shows the importance of this BARD1 attribute in end resection, both in vitro and in cells. Thus, BRCA1–BARD1 enhances the efficiency of all three long-range DNA end resection pathways during homologous recombination in human cells.

通过同源重组进行 DNA 双链断裂修复的许可步骤需要切除 DNA 末端以生成单链 DNA 模板，用于组装由 RAD51 重组酶和辅助因子组成的修复机制¹。DNA 末端切除在机制上错综复杂，并且依赖于肿瘤抑制因子复合物 BRCA1-BARD1（参考文献 ²）。具体来说，三种不同的核酸酶实体——5'–3'核酸外切酶 EXO1 和 DNA 核酸内切酶 DNA2 的异二聚体复合物，与 BLM 或 WRN 解旋酶——协同作用执行末端切除过程³。一个主要问题是 BRCA1-BARD1 是否直接调节终末切除。在这里，使用高度纯化的蛋白质因子，我们提供了 BRCA1-BARD1 与 EXO1、BLM 和 WRN 物理相互作用的证据。重要的是，通过重组的生化系统和单分子分析工具，我们表明 BRCA1-BARD1 上调所有三种切除途径的活性。我们还证明 BRCA1 和 BARD1 包含有助于 BRCA1-BARD1 整体功能的独立模块。此外，对 DNA 结合受损的 BARD1 突变体的分析表明，该 BARD1 属性在体外和细胞终末切除中的重要性。因此，BRCA1-BARD1 在人细胞同源重组过程中增强了所有三种长程 DNA 末端切除途径的效率。