Danilowicz Claudia, Meron Athalia, Prentiss Mara
Department of Physics, Harvard University, Cambridge, MA 02138, United States.
Nucleic Acids Res. 2025 May 10;53(9). doi: 10.1093/nar/gkaf426.
Mutations in RecQ family helicases underlie human genetic disorders associated with genomic instability and cancer predisposition, but questions remain about how properly functioning RecQ reduces these deleterious effects. Importantly, some of the deleterious effects may result from incorrect repair of DNA double-strand breaks (DSBs) by recombinase proteins. Displacement loops (D-loops) are three-strand intermediates formed by recombinases during repair of DSB. RecQ helicases might enhance genome stability by disassembling incorrect recombinase-mediated D-loops formed between mismatched sequences and/or between short regions of accidental homology. We used bulk FRET and gel electrophoresis assays to probe the effects of RecQ family helicases in the context of ongoing recombinase-mediated D-loop formation. We found that RecQ does not differentially promote disassembly of short D-loops or D-loops that include mismatched base pairs. Thus, RecQ does not reduce genomic instability by discriminating against incorrect D-loops. In contrast, our results suggest that RecQ intervenes during D-loop formation to limit the length of recombinase-mediated D-loops. Without that intervention, D-loops can become so long that they do not spontaneously reverse. We suggest that RecQ prevents undesirable long-lived connections between chromosomes that could compromise chromosome metabolism and/or segregation and promote genomic instability.
RecQ家族解旋酶的突变是导致与基因组不稳定和癌症易感性相关的人类遗传疾病的基础，但关于正常功能的RecQ如何减少这些有害影响仍存在疑问。重要的是，一些有害影响可能是由重组酶蛋白对DNA双链断裂（DSB）的错误修复导致的。置换环（D环）是重组酶在DSB修复过程中形成的三链中间体。RecQ解旋酶可能通过拆解在错配序列之间和/或偶然同源性的短区域之间形成的错误的重组酶介导的D环来增强基因组稳定性。我们使用体相荧光共振能量转移（FRET）和凝胶电泳分析来探究RecQ家族解旋酶在正在进行的重组酶介导的D环形成过程中的作用。我们发现，RecQ不会差异性地促进短D环或包含错配碱基对的D环的拆解。因此，RecQ不会通过区分错误的D环来降低基因组不稳定性。相反，我们的结果表明，RecQ在D环形成过程中进行干预，以限制重组酶介导的D环的长度。没有这种干预，D环可能会变得很长，以至于它们不会自发逆转。我们认为，RecQ可防止染色体之间形成不良的长期连接，这种连接可能会损害染色体代谢和/或分离，并促进基因组不稳定。
