BCDX2–CX3 and DX2–CX3 complexes assemble and stabilise RAD51 filaments
Article Date: 02 March 2026
Article URL: https://www.nature.com/articles/s41586-026-10314-z
Article Image: Journal header image
Summary
This study reveals how the five human RAD51 paralogs (RAD51B, RAD51C, RAD51D, XRCC2, XRCC3) assemble into higher-order complexes that build and stabilise RAD51 nucleoprotein filaments during homologous recombination (HR). Using cryo-EM and biochemical experiments the authors show an ATP-dependent BCDX2–CX3 supercomplex bound to single-stranded DNA (ssDNA) that provides a contiguous protofilament template for RAD51. They also identify a RAD51B-independent DX2–CX3 assembly (RAD51D–XRCC2–RAD51C–XRCC3) that acts as a stable RAD51 anchor and can cap filament segments. Differential ATPase regulation defines a dynamic BCDX2–CX3 ‘loader’ and a stable DX2–CX3 ‘anchor’, giving mechanistic modularity to RAD51 filament assembly and offering an atomic framework to interpret disease-causing paralog mutations.
Key Points
- All five RAD51 paralogs can form an ATP-dependent BCDX2–CX3 supercomplex on ssDNA that templates RAD51 filament formation.
- A distinct DX2–CX3 complex (RAD51D–XRCC2–RAD51C–XRCC3) functions as a RAD51 anchor on ssDNA and can cap filament segments.
- Cryo-EM structures show the CX3 module stacked atop BCDX2, creating a contiguous protofilament scaffold for RAD51.
- ATPase activity differentiates a dynamic BCDX2–CX3 ‘loader’ from a stable DX2–CX3 ‘anchor’, providing functional modularity to HR.
- The atomic models enable interpretation of pathogenic paralog variants and link structural defects to genomic instability and cancer risk.
Context and relevance
Homologous recombination is central to repairing DNA double-strand breaks; RAD51 filament formation is the key step. Mutations in RAD51 paralogs are implicated in cancer predisposition and genetic disorders. By providing atomic-resolution structures and a unified mechanistic model, this work resolves long-standing questions about how paralog complexes cooperate and how ATPase activity controls different functional states. The findings are important for researchers in DNA repair, structural biology, cancer genetics and anyone interested in targeting HR pathways therapeutically.
Author style
Punchy: This is a structural and mechanistic breakthrough. The paper delivers atomic blueprints and a clear loader-versus-anchor model — the kind of detail that makes interpreting patient variants and designing follow-up experiments straightforward. If HR or RAD51 biology matters to you, the figures are gold.
Why should I read this?
Short answer: because it finally shows — in atomic detail — how the RAD51 helpers build and hold the filaments that fix broken DNA. It’s a neat unpacking of a messy problem: who assembles, who anchors, and how ATP switches the behaviour. If you care about how paralog mutations give rise to cancer risk or want clear structural maps to guide experiments or drug design, this saves you time and gives you the maps.