GO:0033065 Rad51C-XRCC3 complex: Components, Assembly and Research Methods, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0033065 (Rad51C-XRCC3 complex) is a DNA recombinase mediator complex containing the RAD51 paralogs RAD51C and XRCC3.
• The complex is also known as the CX3 complex, and its yeast and fungal orthologs are called Rad55-Rad57 and Rhp55-Rhp57.
• RAD51C and XRCC3 form a stable heterodimer that stimulates RAD51-mediated homologous recombination and helps localize RAD51 to DNA damage sites.
• XRCC3 ATPase activity is required for normal complex dynamics and homologous recombination.
• The CX3 complex interacts with BRCA2 and regulates FANCM-mediated R-loop resolution to safeguard genome integrity.
• Pathogenic variants in RAD51C and XRCC3 are associated with cancer predisposition, including breast and ovarian cancer, and the complex is a target for functional variant classification.
Description
The Rad51C-XRCC3 complex (GO:0033065) is a conserved DNA recombinase mediator complex that contains the RAD51 paralogs RAD51C and XRCC3, or their orthologs. It is one of several RAD51 paralog-containing complexes that assist the central recombinase RAD51 during homologous recombination and DNA repair. The complex is also referred to as the CX3 complex, and in budding yeast and fission yeast its orthologous complexes are known as Rad55-Rad57 and Rhp55-Rhp57, respectively. Because homologous recombination is essential for genome maintenance, the Rad51C-XRCC3 complex has become a focal point for studies of DNA repair mechanisms, cancer predisposition, and therapeutic targeting. This article summarizes the authoritative GO definition, the molecular and cellular functions of the complex, its roles in disease, and the experimental models and methods used to study it, based strictly on published literature.
Rad51C-XRCC3 complex At A Glance
| GO ID | GO:0033065 |
|---|---|
| GO term | Rad51C-XRCC3 complex |
| Ontology | cellular_component |
| Synonym | CX3 complex; Rad55-Rad57 complex; Rhp55-Rhp57 complex |
| Major function | DNA recombinase mediator complex that stimulates RAD51-mediated homologous recombination and DNA repair |
| Key subunits | RAD51C and XRCC3 (RAD51 paralogs) |
| Conservation | Orthologs exist in yeast (Rad55-Rad57) and other eukaryotes |
| Associated processes | Homologous recombination, DNA double-strand break repair, R-loop resolution, replication fork protection |
| Disease links | Cancer predisposition, including breast and ovarian cancer |
What Is GO:0033065?
According to the Gene Ontology, GO:0033065 (Rad51C-XRCC3 complex) is a DNA recombinase mediator complex that contains the Rad51 paralogs RAD51C and XRCC3, or orthologs thereof. In other words, it is a protein complex that helps the main recombinase RAD51 carry out DNA strand exchange during homologous recombination and DNA repair.
Why Is Rad51C-XRCC3 complex Important in Cell Biology?
The Rad51C-XRCC3 complex is important because it is a core mediator of homologous recombination, a high-fidelity DNA repair pathway that maintains genome stability. Defects in this complex lead to impaired RAD51 loading, sensitivity to DNA-damaging agents, and accumulation of genomic instability, which are hallmarks of cancer. Moreover, the complex is a target for functional classification of variants of uncertain significance in cancer predisposition genes, and it is being explored as a therapeutic vulnerability in tumors with homologous recombination deficiency.
• It is essential for homologous recombination and DNA double-strand break repair.
• It stimulates RAD51-mediated DNA strand exchange and helps localize RAD51 to damage sites.
• It regulates FANCM-mediated R-loop resolution to safeguard genome integrity.
• It interacts with BRCA2, linking it to the BRCA pathway.
• Mutations in RAD51C and XRCC3 are associated with cancer predisposition, including breast and ovarian cancer.
• It is a model for studying RAD51 paralog complexes and their assembly.
• It is a potential target for cancer therapy, especially in homologous recombination-deficient tumors.
• It is used in functional assays to classify variants of uncertain significance.
• It is conserved across eukaryotes, enabling studies in yeast, plants, and human cells.
• It is a component of the DNA damage response network that maintains replication fork stability.
Structure and Composition of Rad51C-XRCC3 complex
RAD51C and XRCC3 heterodimer
In simple terms: The complex is made of two proteins, RAD51C and XRCC3, that stick together.
The Rad51C-XRCC3 complex is a heterodimer of the RAD51 paralogs RAD51C and XRCC3. Complex formation between human RAD51C and XRCC3 was demonstrated by biochemical and cellular assays, and the two proteins co-purify as a stable complex. This heterodimer is the defining component of GO:0033065.
ATPase activity of XRCC3
In simple terms: XRCC3 can burn energy (ATP) to change shape and do its job.
XRCC3 possesses ATPase activity, and this activity is required for normal XRCC3-Rad51C complex dynamics and homologous recombination. Mutations that impair XRCC3 ATPase activity affect the complex's ability to support recombination.
Conservation and orthologs
In simple terms: Similar complexes exist in yeast and plants, so we can study them in simple organisms.
The Rad51C-XRCC3 complex is conserved across eukaryotes. In budding yeast, the orthologous complex is known as Rad55-Rad57, and in fission yeast as Rhp55-Rhp57. In Arabidopsis, RAD51, RAD51C, and XRCC3 proteins form a complex that facilitates RAD51 localization on chromosomes for meiotic recombination.
Interaction with BRCA2 and other partners
In simple terms: The complex talks to other DNA repair proteins to get the job done.
The CX3 complex interacts with BRCA2, a key homologous recombination protein. This interaction links the Rad51C-XRCC3 complex to the broader BRCA-mediated DNA repair network. Additionally, the complex regulates FANCM-mediated R-loop resolution, indicating functional crosstalk with the Fanconi anemia pathway.
Structural insights from cancer mutations
In simple terms: Looking at the 3D shape of the complex helps explain why some mutations cause cancer.
Structural studies of the RAD51C-XRCC3 complex, combined with analysis of cancer patient mutations, have defined its roles in DNA replication. These studies provide a framework for understanding how missense variants in RAD51C and XRCC3 affect complex function and contribute to disease.
Key Genes Involved in GO:0033065 Rad51C-XRCC3 complex
The following genes and proteins are key components or interactors of the Rad51C-XRCC3 complex (GO:0033065).
| Gene | Major Role | Research Relevance |
|---|---|---|
| RAD51C | Core subunit of the Rad51C-XRCC3 complex; RAD51 paralog | Cancer predisposition gene; variants of uncertain significance studied functionally |
| XRCC3 | Core subunit of the Rad51C-XRCC3 complex; ATPase | Cancer predisposition gene; ATPase activity required for complex dynamics |
| RAD51 | Central recombinase stimulated by the complex | Target of mediator complexes; localization on chromosomes |
| BRCA2 | Interacts with CX3 complex; homologous recombination factor | Links CX3 to BRCA pathway; therapeutic target |
| FANCM | R-loop resolution factor regulated by CX3 | Genome integrity maintenance; crosstalk with Fanconi anemia |
| RAD51B | RAD51 paralog; part of BCDX2 complex | Interacts with CX3 and BRCA2 |
| RAD51D | RAD51 paralog; part of BCDX2 complex | Interacts with CX3 and BRCA2 |
| XRCC2 | RAD51 paralog; part of BCDX2 complex | Interacts with CX3 and BRCA2 |
| RAD55 (yeast) | Ortholog of RAD51C in budding yeast | Model for Rad51C-XRCC3 complex studies |
| RAD57 (yeast) | Ortholog of XRCC3 in budding yeast | Model for Rad51C-XRCC3 complex studies |
| Rhp55 (fission yeast) | Ortholog of RAD51C in fission yeast | Model for Rad51C-XRCC3 complex studies |
| Rhp57 (fission yeast) | Ortholog of XRCC3 in fission yeast | Model for Rad51C-XRCC3 complex studies |
| AtRAD51C (Arabidopsis) | Plant ortholog of RAD51C | Meiotic recombination studies |
| AtXRCC3 (Arabidopsis) | Plant ortholog of XRCC3 | Meiotic recombination studies |
| AtRAD51 (Arabidopsis) | Plant RAD51 recombinase | Localization on chromosomes |
| PALB2 | BRCA2 partner and homologous recombination factor | Potential link to CX3 complex |
| BARD1 | BRCA1 partner; DNA repair | Potential crosstalk with CX3 |
| BRCA1 | Homologous recombination and DNA repair | Potential crosstalk with CX3 |
How Is Rad51C-XRCC3 complex Regulated?
The Rad51C-XRCC3 complex is regulated at multiple levels. XRCC3 ATPase activity is required for normal complex dynamics and homologous recombination, indicating that nucleotide binding and hydrolysis modulate its function. The complex interacts with BRCA2, which may regulate its localization or activity during homologous recombination. Additionally, the complex regulates FANCM-mediated R-loop resolution, suggesting that it is part of a regulatory circuit that prevents R-loop accumulation and maintains genome integrity. Post-translational modifications and cell cycle-dependent expression may also influence its activity, although specific mechanisms are still being elucidated.
Rad51C-XRCC3 complex and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| RAD51C | Breast and ovarian cancer predisposition | Knockout or point-mutation cell lines; variant functional assays |
| XRCC3 | Cancer predisposition; radiosensitivity | Knockout or ATPase-dead point-mutant models |
| BRCA2 | Breast and ovarian cancer; Fanconi anemia | Knockout or knock-in models to study CX3 interaction |
| FANCM | Fanconi anemia; R-loop-associated genome instability | Knockout or overexpression models to study R-loop resolution |
| RAD51C/XRCC3 | Homologous recombination deficiency | Isogenic knockout and rescue models for drug sensitivity |
Cancer predisposition
Pathogenic variants in RAD51C and XRCC3 are associated with increased risk of breast and ovarian cancer. Functional characterization of variants of uncertain significance in RAD51C has identified a hotspot for inactivating missense variants, highlighting the clinical importance of the Rad51C-XRCC3 complex in cancer predisposition. Comprehensive analysis of cancer variants in RAD51C has revealed a homologous recombination-deficient mutation cluster, further linking the complex to tumorigenesis.
Homologous recombination deficiency and therapy
Tumors with defects in the Rad51C-XRCC3 complex exhibit homologous recombination deficiency, which can be exploited therapeutically with PARP inhibitors or platinum-based chemotherapy. Understanding the structural and functional consequences of patient mutations in the complex helps predict response to these therapies.
Genome instability and R-loop regulation
The Rad51C-XRCC3 complex regulates FANCM-mediated R-loop resolution, and its loss leads to R-loop accumulation and genome instability. This function is critical for safeguarding genome integrity and may contribute to the etiology of cancers associated with complex dysfunction.
From Rad51C-XRCC3 complex-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the role of RAD51C in homologous recombination? | RAD51C knockout cell lines (e.g., HEK293T, U2OS) |
| How do cancer-associated missense variants affect complex function? | Point-mutation knock-in cell lines expressing RAD51C or XRCC3 variants |
| Does XRCC3 ATPase activity regulate complex dynamics? | ATPase-dead point-mutant XRCC3 knock-in models |
| How does the complex interact with BRCA2? | Tagged knock-in of RAD51C or XRCC3 for co-immunoprecipitation |
| What is the effect of RAD51C overexpression on DNA repair? | Overexpression cell lines and xenograft models |
| How does the complex regulate R-loop resolution? | Knockout or overexpression of RAD51C/XRCC3 combined with R-loop detection |
How to Study the Rad51C-XRCC3 complex Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Co-immunoprecipitation | Protein-protein interaction | Detecting RAD51C-XRCC3 heterodimer |
| ATPase assay | ATP hydrolysis | Measuring XRCC3 catalytic activity |
| DNA strand exchange assay | Recombination activity | Testing complex function with RAD51 |
| Clonogenic survival assay | Cell sensitivity to DNA damage | Assessing homologous recombination proficiency |
| Immunofluorescence | RAD51 foci and R-loop formation | Localization and genome integrity |
| Structural biology (cryo-EM, crystallography) | 3D structure of complex | Mapping patient mutations |
| CRISPR knockout screening | Gene essentiality and drug response | Identifying synthetic lethal interactions |
| Variant functional assays | Impact of missense variants | Classifying variants of uncertain significance |
Biochemical reconstitution and pull-down assays
Complex formation between RAD51C and XRCC3 can be studied using co-immunoprecipitation, pull-down assays, and size-exclusion chromatography. These methods help determine whether variants affect heterodimerization.
ATPase and DNA strand exchange assays
XRCC3 ATPase activity can be measured using ATP hydrolysis assays, and the effect of the complex on RAD51-mediated DNA strand exchange can be tested using in vitro recombination assays.
Cellular sensitivity assays
Knockout or point-mutant cell lines can be tested for sensitivity to DNA-damaging agents such as mitomycin C, cisplatin, or PARP inhibitors to assess homologous recombination proficiency.
Structural and imaging approaches
Structural studies of the RAD51C-XRCC3 complex, combined with fluorescence microscopy to visualize RAD51 foci and R-loops, provide insights into its mechanism and regulation.
How CRISPR Can Be Used to Study GO:0033065 Rad51C-XRCC3 complex
Knockout
CRISPR knockout of RAD51C or XRCC3 can be used to create isogenic cell lines to study homologous recombination deficiency, DNA damage sensitivity, and synthetic lethality with PARP inhibitors. These models are valuable for validating the role of the Rad51C-XRCC3 complex in genome maintenance.
Point Mutation
Point mutations identified in cancer patients, such as those in RAD51C or XRCC3, can be introduced using CRISPR base editing or homology-directed repair to study their functional impact on complex assembly, ATPase activity, and DNA repair. Such models help classify variants of uncertain significance.
Knock-in
Knock-in of tagged RAD51C or XRCC3 (e.g., GFP, HA, or BirA tags) allows for affinity purification, imaging, and interactome studies of the Rad51C-XRCC3 complex in its native context. This approach can reveal dynamic interactions with BRCA2 and other partners.
Overexpression
Overexpression of RAD51C or XRCC3 can be used to study the effects of elevated complex levels on DNA repair, replication fork stability, and chemoresistance. Such models may also help identify dominant-negative effects of mutant alleles.
How EDITGENE Supports Rad51C-XRCC3 complex Research
Researchers studying Rad51C-XRCC3 complex-related genes often need to determine whether a candidate gene is causally involved in DNA repair, genome stability, or cancer predisposition. EDITGENE provides a comprehensive suite of CRISPR-based services to create precisely engineered cell models for such studies.
Contact EDITGENE today to design your custom CRISPR model for Rad51C-XRCC3 complex research.
Frequently Asked Questions About Rad51C-XRCC3 complex
What is the Rad51C-XRCC3 complex?
The Rad51C-XRCC3 complex (GO:0033065) is a DNA recombinase mediator complex containing the RAD51 paralogs RAD51C and XRCC3, which stimulates RAD51-mediated homologous recombination.
What genes are involved in the Rad51C-XRCC3 complex?
The core genes are RAD51C and XRCC3; other associated genes include RAD51, BRCA2, and FANCM.
What is the function of the Rad51C-XRCC3 complex?
It functions as a mediator complex that stimulates RAD51-mediated DNA strand exchange and helps localize RAD51 to DNA damage sites during homologous recombination.
What diseases are associated with Rad51C-XRCC3 complex mutations?
Mutations in RAD51C and XRCC3 are associated with cancer predisposition, including breast and ovarian cancer, and with homologous recombination deficiency.
How is the Rad51C-XRCC3 complex regulated?
XRCC3 ATPase activity is required for complex dynamics, and the complex interacts with BRCA2 and regulates FANCM-mediated R-loop resolution.
What is the CX3 complex?
CX3 complex is a synonym for the Rad51C-XRCC3 complex, reflecting its two core subunits.
What are the yeast orthologs of the Rad51C-XRCC3 complex?
In budding yeast, the orthologous complex is Rad55-Rad57; in fission yeast, it is Rhp55-Rhp57.
How can I study the Rad51C-XRCC3 complex using CRISPR?
CRISPR knockout, point mutation, knock-in, and overexpression models can be used to study its role in DNA repair and cancer.
What methods are used to study the Rad51C-XRCC3 complex?
Common methods include co-immunoprecipitation, ATPase assays, DNA strand exchange assays, immunofluorescence, and structural biology.
Why is the Rad51C-XRCC3 complex important for genome stability?
It regulates R-loop resolution and homologous recombination, preventing genome instability and cancer.
Conclusion
The Rad51C-XRCC3 complex (GO:0033065) is a conserved DNA recombinase mediator complex essential for homologous recombination and genome stability. Its core subunits, RAD51C and XRCC3, form a heterodimer that stimulates RAD51 and interacts with BRCA2 and FANCM to maintain genome integrity. Mutations in these genes are linked to cancer predisposition, making the complex a critical target for functional variant classification and therapeutic development. Continued research using CRISPR models and biochemical assays will further elucidate its mechanisms and disease relevance.
References
- 1. Sahoo S et al.. 2026. RAD51C-XRCC3 complex regulates FANCM-mediated R-loop resolution to safeguard genome integrity.. Sci Adv 12(8):eaea5932 PMID: 41719405
- 2. 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
- 3. 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
- 4. Su H et al.. 2017. Arabidopsis RAD51, RAD51C and XRCC3 proteins form a complex and facilitate RAD51 localization on chromosomes for meiotic recombination.. PLoS Genet 13(5):e1006827 PMID: 28562599
- 5. Yamada NA et al.. 2004. XRCC3 ATPase activity is required for normal XRCC3-Rad51C complex dynamics and homologous recombination.. J Biol Chem 279(22):23250-4 PMID: 15037616
- 6. Masson JY et al.. 2001. Complex formation by the human RAD51C and XRCC3 recombination repair proteins.. Proc Natl Acad Sci U S A 98(15):8440-6 PMID: 11459987
- 7. Longo MA et al.. 2023. RAD51C-XRCC3 structure and cancer patient mutations define DNA replication roles.. Nat Commun 14(1):4445 PMID: 37488098
- 8. Thrasher JG et al.. 2024. RAD51 Paralogs and RAD51 Paralog Complexes BCDX2 and CX3 Interact with BRCA2.. bioRxiv PMID: 39416194
