GO:0033063 Rad51B-Rad51C-Rad51D-XRCC2 complex: Components, Assembly and Research Methods, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0033063 describes the Rad51B-Rad51C-Rad51D-XRCC2 complex, also known as BCDX2, a DNA recombinase mediator complex containing the RAD51 paralogs RAD51B, RAD51C, RAD51D, and XRCC2.
• The BCDX2 complex is a tumour suppressor whose structure and function have been resolved by cryo-electron microscopy, revealing how it binds and stabilizes RAD51 filaments.
• BCDX2 interacts with BRCA2 and other RAD51 paralog complexes such as CX3 to assemble and stabilize RAD51 filaments during homologous recombination.
• Mutations in RAD51C, a core subunit of BCDX2, are associated with cancer predisposition and include inactivating missense variants that disrupt complex function.
• BCDX2 is essential for homologous recombination repair, replication fork protection, and genome stability, and its loss leads to sensitivity to DNA-damaging agents.
• Researchers study BCDX2 using CRISPR knockout, point-mutation knock-in, structural biology, and functional assays to dissect its role in DNA repair and cancer.
Description
The Rad51B-Rad51C-Rad51D-XRCC2 complex (GO:0033063), commonly referred to as BCDX2, is a heterotetrameric DNA recombinase mediator complex that contains the RAD51 paralogs RAD51B, RAD51C, RAD51D, and XRCC2. This complex is a key player in homologous recombination (HR), a high-fidelity DNA repair pathway that maintains genome stability and is essential for tumor suppression. The BCDX2 complex functions by facilitating the assembly and stabilization of RAD51 nucleoprotein filaments on single-stranded DNA, a critical step in HR. Dysregulation of BCDX2 components, particularly RAD51C, has been linked to cancer predisposition and is observed in breast and ovarian cancers. The structural and functional characterization of BCDX2 has been advanced by recent cryo-electron microscopy studies, which revealed how the complex interacts with RAD51 filaments and with other mediator complexes such as CX3. Understanding the molecular architecture and regulation of BCDX2 is therefore of significant interest for cancer biology and for the development of targeted therapies. This article provides a comprehensive overview of GO:0033063, covering its definition, composition, biological roles, associated diseases, and the experimental models and methods used to study it. All statements are based on published literature and authoritative GO annotations.
Rad51B-Rad51C-Rad51D-XRCC2 complex At A Glance
| GO ID | GO:0033063 |
|---|---|
| GO term | Rad51B-Rad51C-Rad51D-XRCC2 complex |
| Ontology | cellular_component |
| Synonym | BCDX2 complex |
| Major function | DNA recombinase mediator activity in homologous recombination; stabilizes RAD51 filaments |
| Subunits | RAD51B, RAD51C, RAD51D, XRCC2 |
| Associated diseases | Cancer predisposition, particularly breast and ovarian cancer linked to RAD51C mutations |
| Interacting partners | BRCA2, CX3 complex (RAD51C-XRCC3), DX2 complex |
What Is GO:0033063?
GO:0033063 is a Gene Ontology cellular component term that defines a DNA recombinase mediator complex containing the RAD51 paralogs RAD51B, RAD51C, RAD51D, and XRCC2, or their orthologs. The complex is also known as BCDX2 and functions as a mediator of homologous recombination by promoting the assembly of RAD51 filaments on DNA.
Why Is Rad51B-Rad51C-Rad51D-XRCC2 complex Important in Cell Biology?
The Rad51B-Rad51C-Rad51D-XRCC2 complex is critical for homologous recombination, a pathway that ensures accurate DNA repair and genome stability. Its dysfunction leads to impaired RAD51 filament formation, accumulation of DNA damage, and increased cancer risk. Understanding BCDX2 provides insights into tumor suppressor mechanisms and offers potential targets for cancer therapy, especially for tumors with defects in HR.
• Essential for homologous recombination repair and genome maintenance.
• Acts as a tumour suppressor; mutations in RAD51C are linked to breast and ovarian cancer.
• Stabilizes RAD51 filaments on single-stranded DNA, a key step in HR.
• Interacts with BRCA2 and other RAD51 paralog complexes to coordinate repair.
• Loss of BCDX2 function confers sensitivity to DNA-damaging agents like PARP inhibitors.
• Provides a model for studying RAD51 paralog complexes and their roles in replication fork protection.
• Involved in replication fork reversal in coordination with HELQ and BRCA2 pathways.
• Structural insights from cryo-EM enable rational design of inhibitors or targeted therapies.
Structure and Composition of Rad51B-Rad51C-Rad51D-XRCC2 complex
Overall architecture of the BCDX2 complex
In simple terms: The BCDX2 complex is a four-protein machine that helps repair broken DNA.
The BCDX2 complex is a heterotetramer composed of RAD51B, RAD51C, RAD51D, and XRCC2, which assemble into a ring-like structure that binds DNA. Cryo-electron microscopy studies have revealed that the complex forms a dimer of dimers, with RAD51C and RAD51D forming a central core and RAD51B and XRCC2 at the periphery. This architecture is essential for its mediator function in homologous recombination.
RAD51C as a catalytic and structural hub
In simple terms: RAD51C is the central piece that holds the complex together and is often mutated in cancer.
RAD51C is a core subunit of BCDX2 and is frequently mutated in cancer. It contains Walker A and B motifs for ATP binding and hydrolysis, and its missense variants can disrupt complex assembly and function. Comprehensive analysis of cancer variants identified a hotspot for inactivating missense mutations in RAD51C, highlighting its critical role.
Assembly and stabilization of RAD51 filaments
In simple terms: BCDX2 helps RAD51 proteins coat DNA to form a protective filament that repairs damage.
BCDX2 promotes the assembly of RAD51 filaments on single-stranded DNA by mediating the nucleation and extension steps. It interacts with BRCA2 and other RAD51 paralog complexes such as CX3 to stabilize the filament and prevent disassembly. Recent cryo-EM studies visualized how XRCC3-RAD51C-RAD51D-XRCC2 (CX3) caps and stabilizes RAD51 filaments.
Interaction with other mediator complexes
In simple terms: BCDX2 works together with other protein complexes to efficiently repair DNA.
BCDX2 interacts with the CX3 complex (RAD51C-XRCC3) and the DX2 complex (RAD51D-XRCC2) to form higher-order assemblies that stabilize RAD51 filaments. These interactions are coordinated with BRCA2 and are essential for homologous recombination and replication fork protection.
Key Genes Involved in GO:0033063 Rad51B-Rad51C-Rad51D-XRCC2 complex
The following genes encode the core subunits and key interactors of the Rad51B-Rad51C-Rad51D-XRCC2 complex, based on published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| RAD51B | Subunit of BCDX2; mediates RAD51 filament assembly | Mutations linked to cancer; structural studies |
| RAD51C | Core subunit; ATPase; interacts with BRCA2 | Hotspot for cancer-associated missense variants |
| RAD51D | Subunit of BCDX2; stabilizes complex | Mutations associated with ovarian cancer |
| XRCC2 | Subunit of BCDX2; DNA binding | Defects cause HR deficiency and cancer predisposition |
| BRCA2 | Interacts with BCDX2; delivers RAD51 to ssDNA | Key HR mediator; crosstalk with BCDX2 |
| RAD51 | Central recombinase; forms filaments | Target of BCDX2 mediator activity |
| XRCC3 | Subunit of CX3 complex; interacts with BCDX2 | Stabilizes RAD51 filaments |
| HELQ | DNA helicase; promotes replication fork reversal | Coordinates with BRCA2 and FANCD2 pathways |
| FANCD2 | Fanconi anemia protein; involved in crosslink repair | Functional interplay with BCDX2 |
| PALB2 | BRCA2 partner; links BRCA1 to BRCA2 | Facilitates HR; potential crosstalk |
| RAD51AP1 | RAD51 accessory factor | Stimulates RAD51-mediated strand exchange |
| SWS1 | RAD51 paralog in yeast; similar to RAD51D | Model for BCDX2 studies |
| RAD51C variants | Missense mutations in cancer | Functional characterization |
| RAD51B fusions | Oncogenic fusions in melanoma | Potential therapeutic target |
| XRCC2 mutations | Defective HR | Biomarker for PARP inhibitor sensitivity |
| RAD51D mutations | Ovarian cancer risk | Clinical genetic testing |
| BCDX2 complex | Heterotetrameric mediator | Structural and functional studies |
How Is Rad51B-Rad51C-Rad51D-XRCC2 complex Regulated?
The Rad51B-Rad51C-Rad51D-XRCC2 complex is regulated at multiple levels, including its assembly, post-translational modifications, and interactions with other HR factors. Its formation is cell-cycle dependent, with peak assembly in S/G2 phase when homologous recombination is active. BRCA2 and other mediator complexes such as CX3 modulate its activity and stability. Additionally, the DNA helicase HELQ coordinates with BRCA2 and FANCD2 pathways to promote replication fork reversal, indirectly influencing BCDX2 function.
Rad51B-Rad51C-Rad51D-XRCC2 complex and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| RAD51C | Breast and ovarian cancer; HRD | CRISPR knockout in cancer cell lines; point mutations |
| RAD51D | Ovarian cancer predisposition | Knockout and knock-in models |
| XRCC2 | HR deficiency; cancer susceptibility | CRISPR knockout; functional assays |
| RAD51B | Cancer; melanoma fusions | Overexpression and knockout models |
| BRCA2 | Breast/ovarian cancer; Fanconi anemia | Conditional knockout; interaction studies |
Cancer predisposition and RAD51C mutations
Germline mutations in RAD51C, a core subunit of BCDX2, are associated with increased risk of breast and ovarian cancer. Functional characterization of variants of uncertain significance identified a hotspot for inactivating missense variants in RAD51C, which impair complex assembly and HR. These findings support the inclusion of RAD51C in genetic testing panels for hereditary cancer.
Homologous recombination deficiency and therapy response
Tumors with defects in BCDX2 components exhibit homologous recombination deficiency (HRD), making them sensitive to PARP inhibitors and platinum-based chemotherapy. Loss of RAD51C or XRCC2 function leads to impaired RAD51 filament formation and increased sensitivity to DNA-damaging agents. Thus, BCDX2 status can serve as a biomarker for HRD and guide treatment decisions.
Replication fork protection and genome stability
BCDX2 plays a role in protecting stalled replication forks and promoting fork reversal in coordination with HELQ and BRCA2. Defects in this pathway lead to fork degradation and genome instability, contributing to cancer development. Understanding these mechanisms may reveal new therapeutic targets for HR-deficient tumors.
From Rad51B-Rad51C-Rad51D-XRCC2 complex-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of RAD51C impair HR? | CRISPR knockout in U2OS or HeLa cells |
| Do missense variants affect complex assembly? | Point-mutation knock-in of RAD51C variants |
| How does BCDX2 interact with BRCA2? | Tagged knock-in (e.g., GFP) and co-IP |
| Can overexpression rescue HR defect? | Overexpression of wild-type or mutant RAD51C |
| What is the structural basis of filament stabilization? | Cryo-EM of purified BCDX2 and RAD51 filaments |
| Does BCDX2 loss sensitize to PARP inhibitors? | Knockout cell lines treated with olaparib |
How to Study the Rad51B-Rad51C-Rad51D-XRCC2 complex Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Cryo-EM | 3D structure of protein complexes | Visualizing BCDX2 and RAD51 filaments |
| DR-GFP reporter assay | Homologous recombination efficiency | Assessing HR in knockout cells |
| Co-immunoprecipitation | Protein-protein interactions | Studying BCDX2-BRCA2 interaction |
| Western blot | Protein expression and stability | Validating knockout or overexpression |
| Immunofluorescence | Subcellular localization and foci formation | RAD51 foci formation after DNA damage |
| RNA-seq | Transcriptome changes | Identifying HRD signatures |
| Proteomics | Protein abundance and modifications | Global analysis of BCDX2 interactome |
| CRISPR screening | Gene essentiality and synthetic lethality | Identifying modifiers of BCDX2 loss |
Structural biology (cryo-EM)
Cryo-electron microscopy has been instrumental in resolving the structure of the BCDX2 complex and its interaction with RAD51 filaments. These studies revealed the architecture of the complex and how it stabilizes RAD51 nucleoprotein filaments, providing a framework for understanding disease mutations.
Functional assays for homologous recombination
HR efficiency can be measured using reporter assays (e.g., DR-GFP) in cells with CRISPR knockout or point mutations in BCDX2 subunits. These assays quantify the ability of cells to repair double-strand breaks by HR and assess the impact of specific variants.
Protein interaction studies
Co-immunoprecipitation, pull-down assays, and proximity ligation assays are used to study interactions between BCDX2 subunits and partners like BRCA2 and CX3. These methods help define the assembly and regulation of the complex.
Genomic and proteomic profiling
RNA-seq and proteomics can reveal global changes in gene expression and protein abundance upon BCDX2 loss or mutation. Such studies identify pathways that compensate for or depend on BCDX2 function.
How CRISPR Can Be Used to Study GO:0033063 Rad51B-Rad51C-Rad51D-XRCC2 complex
Knockout
CRISPR knockout of RAD51C, RAD51D, XRCC2, or RAD51B in cell lines abrogates BCDX2 function, leading to HR deficiency and sensitivity to DNA-damaging agents. These models are used to study the role of BCDX2 in DNA repair and to validate synthetic lethal interactions.
Point Mutation
Point mutations identified in cancer patients, such as RAD51C missense variants, can be introduced via CRISPR knock-in to assess their impact on complex assembly and HR activity. This approach helps classify variants of uncertain significance.
Knock-in
Tagged knock-in of BCDX2 subunits (e.g., GFP or HA) allows for visualization and purification of the complex from cells. This enables detailed biochemical and structural studies of the endogenous complex.
Overexpression
Overexpression of wild-type or mutant BCDX2 subunits can be used to rescue knockout phenotypes or to study dominant-negative effects. This is useful for dissecting the contribution of individual subunits to HR.
How EDITGENE Supports Rad51B-Rad51C-Rad51D-XRCC2 complex Research
Researchers studying Rad51B-Rad51C-Rad51D-XRCC2 complex-related genes often need to determine whether a candidate gene is causally involved in homologous recombination, cancer predisposition, or therapy response. EDITGENE provides a comprehensive suite of CRISPR services to enable such investigations, from gene knockout to precise point mutations and library screening.
Contact EDITGENE today to design your custom CRISPR model for Rad51B-Rad51C-Rad51D-XRCC2 complex research.
Frequently Asked Questions About Rad51B-Rad51C-Rad51D-XRCC2 complex
What is the Rad51B-Rad51C-Rad51D-XRCC2 complex?
It is a DNA recombinase mediator complex, also known as BCDX2, composed of four RAD51 paralogs that functions in homologous recombination.
What genes are involved in the Rad51B-Rad51C-Rad51D-XRCC2 complex?
The core genes are RAD51B, RAD51C, RAD51D, and XRCC2, which encode the subunits of the complex.
What is the function of GO:0033063?
GO:0033063 describes a cellular component that mediates RAD51 filament assembly during homologous recombination.
How is the BCDX2 complex related to cancer?
Mutations in RAD51C, a subunit of BCDX2, are associated with breast and ovarian cancer predisposition.
What diseases are linked to RAD51C mutations?
RAD51C mutations increase risk of breast and ovarian cancer and cause homologous recombination deficiency.
What is the structure of the BCDX2 complex?
It is a heterotetramer with a ring-like architecture, resolved by cryo-EM, that binds DNA and stabilizes RAD51 filaments.
How does BCDX2 interact with BRCA2?
BCDX2 interacts with BRCA2 to coordinate RAD51 filament assembly and stabilization.
What research methods are used to study BCDX2?
Cryo-EM, CRISPR knockout, point mutation knock-in, co-IP, and HR reporter assays are commonly used.
Can CRISPR be used to model BCDX2 mutations?
Yes, CRISPR knockout and knock-in can create isogenic cell lines with specific mutations for functional studies.
What is the role of XRCC2 in the BCDX2 complex?
XRCC2 is a subunit that binds DNA and is essential for the complex's mediator function in HR.
Conclusion
The Rad51B-Rad51C-Rad51D-XRCC2 complex (GO:0033063) is a central mediator of homologous recombination and a critical tumour suppressor. Its structural and functional characterization has provided deep insights into DNA repair mechanisms and cancer predisposition. Continued research using advanced CRISPR models and structural techniques will further elucidate its regulation and therapeutic potential.
References
- 1. Greenhough LA et al.. 2023. Structure and function of the RAD51B-RAD51C-RAD51D-XRCC2 tumour suppressor.. Nature 619(7970):650-657 PMID: 37344587
- 2. Greenhough LA et al.. 2026. Cryo-electron microscopic visualization of RAD51 filament assembly and end-capping by XRCC3-RAD51C-RAD51D-XRCC2.. Science 391(6788):eaea1546 PMID: 41196948
- 3. Hu C et al.. 2023. Functional and Clinical Characterization of Variants of Uncertain Significance Identifies a Hotspot for Inactivating Missense Variants in RAD51C.. Cancer Res 83(15):2557-2571 PMID: 37253112
- 4. Prakash R et al.. 2022. Homologous recombination-deficient mutation cluster in tumor suppressor RAD51C identified by comprehensive analysis of cancer variants.. Proc Natl Acad Sci U S A 119(38):e2202727119 PMID: 36099300
- 5. Thrasher JG et al.. 2024. RAD51 Paralogs and RAD51 Paralog Complexes BCDX2 and CX3 Interact with BRCA2.. bioRxiv PMID: 39416194
- 6. Koo CW et al.. 2026. BCDX2-CX3 and DX2-CX3 complexes assemble and stabilize RAD51 filaments.. Nature 653(8115):952-961 PMID: 41772053
- 7. Sullivan MR et al.. 2018. RAD-ical New Insights into RAD51 Regulation.. Genes (Basel) 9(12) PMID: 30551670
- 8. Dunbayev Y et al.. 2026. The DNA helicase HELQ promotes replication fork reversal in coordination with BRCA2- and FANCD2-mediated repair pathways.. Nucleic Acids Res 54(8) PMID: 42055550
