Structural insight into how RAD51 paralog exchange regulates RAD51 filament formation
Homologous recombination (HR) repairs DNA double-strand breaks and stabilizes stressed replication forks, and HR deficiency promotes genome instability and cancer. HR requires assembly of RAD51 nucleoprotein filaments on single-stranded DNA (ssDNA), a process regulated by the human RAD51 paralogs RAD51C, XRCC3, RAD51D and XRCC2. Here, using cryo-electron microscopy, we find that the RAD51-XRCC3-RAD51C complex (RAD51-X3C) assembles into an octamer in which XRCC3 engages the RAD51 DNA-binding surface and RAD51 subunits adopt a misaligned configuration incompatible with filament formation. These features define an autoinhibited RAD51-X3C state that limits nonproductive RAD51 binding to double-stranded DNA or RNA-DNA hybrids while preserving RAD51 availability for ssDNA-dependent strand exchange. We further show that the RAD51D-XRCC2 paralog complex remodels RAD51-X3C into a pentameric RAD51-X3CDX2 assembly by engaging the exposed RAD51C surface and disrupting contacts that stabilize the octamer. This remodeling exposes the RAD51 DNA-binding interface, enhances RAD51-ssDNA filament assembly, and promotes strand exchange on RPA-coated ssDNA, and yields a filament-compatible paralog assembly that integrates into ssDNA-bound RAD51 filaments. Together, these findings establish paralog exchange as a mechanism that converts an autoinhibited RAD51-X3C octamer into an activated RAD51-X3CDX2 pentamer to regulate RAD51 filament formation during HR and replication fork preservation.
Authors
- Youngho Kwon (ORCID: https://orcid.org/0000-0002-0287-8795)
- Sahiti Kuppa (ORCID: https://orcid.org/0000-0003-2601-6636)
- Svetla Stoilova‐McPhie (ORCID: https://orcid.org/0000-0002-4626-3581)
- Cody M. Rogers (ORCID: https://orcid.org/0000-0001-6499-1390)
- Eloïse Dray (ORCID: https://orcid.org/0000-0001-6793-9838)
- Robert Hromas (ORCID: https://orcid.org/0000-0002-1916-6276)
- Jeffrey N. Katz (ORCID: https://orcid.org/0000-0003-2104-4670)
- Angela M. Jasper (ORCID: https://orcid.org/0000-0002-9548-8445)
- S Zhou
- Eric C. Greene (ORCID: https://orcid.org/0000-0002-7387-824X)
- David S. Libich (ORCID: https://orcid.org/0000-0001-6492-2803)
- Yashpal Rawal (ORCID: https://orcid.org/0000-0001-9209-788X)
- Shaun K. Olsen (ORCID: https://orcid.org/0000-0002-1265-7101)
- M Prasada Rao
- Digant Nayak (ORCID: https://orcid.org/0000-0003-3680-0846)
- Alexander B. Taylor (ORCID: https://orcid.org/0000-0003-3517-6033)
- Sandeep Burma (ORCID: https://orcid.org/0000-0001-7057-9845)
- Alexander V. Mazin (ORCID: https://orcid.org/0000-0002-5430-9797)
- Elizabeth V. Wasmuth (ORCID: https://orcid.org/0000-0003-1474-4935)
- Kara Anne Bernstein (ORCID: https://orcid.org/0000-0003-2247-6459)
- Lijia Jia
- Qingming Fang (ORCID: https://orcid.org/0000-0002-4006-0636)
- F Zhang
- Patrick Sung (ORCID: https://orcid.org/0000-0003-1396-9040)
- Mohd Azrin Jamalruddin (ORCID: https://orcid.org/0000-0002-7408-6914)
- Daohong Zhou (ORCID: https://orcid.org/0000-0002-2400-6461)
- Lijuan Guo (ORCID: https://orcid.org/0000-0002-0968-9735)
- Shahrez Syed
- Caleb Stratton
- Lorena Samentar
- Miriam Tovar
- Eliza A. Ruben
- Maria Jasin
- Weixing Zhao (ORCID: https://orcid.org/0000-0001-5746-3696)
- Hardeep Kaur
- Jae-Hoon Ji (ORCID: https://orcid.org/0009-0001-8233-9416)
Institutions
- Memorial Sloan Kettering Cancer Center (US)
- Howard Hughes Medical Institute (US)
- The University of Texas at San Antonio Health Science Center (US)
- Cornell University (US)
- Columbia University Irving Medical Center (US)
- University of Pennsylvania (US)
Publication Details
- Journal
- Nature Structural & Molecular Biology
- Published
- 2026-04-22
- DOI
- https://doi.org/10.1038/s41594-026-01796-6
- Citations
- 1
- Primary Topic
- DNA Repair Mechanisms
- Type
- article
- Field-Weighted Citation Impact
- 11.68