GO:0070531 BRCA1-A complex: Components, Assembly and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0070531 describes the BRCA1-A complex, a six-subunit protein assembly built around the BRCA1-BARD1 heterodimer that binds K63-linked polyubiquitin on histone H2A/H2AX at DNA damage sites.
• The complex contains BRCA1, BARD1, RAP80/UIMC1, BRCC3/BRCC36, BRE/BRCC45, FAM175A/CCDC98/Abraxas and MERIT40/NBA1, and its assembly is required for efficient BRCA1 recruitment to lesions.
• BRCC3/BRCC36 is a K63-specific deubiquitylase whose autologous activity within the complex licenses DNA damage recognition and prevents premature disassembly.
• Loss of BRCA1-A function causes defective homologous recombination, replication fork instability, and hypersensitivity to PARP inhibitors and platinum drugs.
• The BRCA1-A complex restricts replication fork reversal-dependent repair in ATM-deficient cells, revealing a synthetic vulnerability that can be exploited therapeutically.
• BRCA1-A and LIG4 complexes cooperate in extrachromosomal DNA biogenesis, linking this complex to drug resistance and cancer genome evolution.
Description
The BRCA1-A complex (GO:0070531) is a multi-subunit cellular component defined by its ability to recognize and bind K63-linked polyubiquitin chains on histone H2A and H2AX at sites of DNA damage. It is a central node in the DNA damage response, acting as a recruitment platform that concentrates the BRCA1-BARD1 heterodimer at lesions to promote homologous recombination and genome stability. Because BRCA1 is a major breast and ovarian cancer susceptibility gene, understanding the composition, assembly, and regulation of the BRCA1-A complex is directly relevant to cancer biology and therapeutic development. The complex is not a static entity; its subunits undergo dynamic post-translational modifications, including K63 deubiquitylation by BRCC3/BRCC36, which regulates its own stability and function. Recent work has also implicated the BRCA1-A complex in restricting replication fork reversal-dependent repair in ATM-deficient cells, suggesting that it shapes repair pathway choice under replication stress. In addition, BRCA1-A cooperates with LIG4 in extrachromosomal DNA biogenesis, a process linked to drug resistance. This article synthesizes the current understanding of the BRCA1-A complex, its genes, its roles in disease, and the experimental methods used to study it.
BRCA1-A complex At A Glance
| GO ID | GO:0070531 |
|---|---|
| GO term | BRCA1-A complex |
| Ontology | cellular_component |
| Synonym | None |
| Major function | Recognition of K63-linked polyubiquitin on histone H2A/H2AX at DNA damage sites and recruitment of BRCA1-BARD1 to promote DNA repair |
| Key subunits | BRCA1, BARD1, RAP80/UIMC1, BRCC3/BRCC36, BRE/BRCC45, FAM175A/CCDC98/Abraxas, MERIT40/NBA1 |
| Associated process | Homologous recombination, DNA damage response, replication fork protection |
| Disease relevance | Breast and ovarian cancer predisposition, PARP inhibitor sensitivity, chemoresistance |
What Is GO:0070531?
The BRCA1-A complex is a protein complex that contains the BRCA1-BARD1 heterodimer together with RAP80/UIMC1, BRCC3/BRCC36, BRE/BRCC45, FAM175A/CCDC98/Abraxas and MERIT40/NBA1. It specifically recognizes and binds K63-linked polyubiquitin chains present on histone H2A and H2AX at DNA damage sites, thereby serving as a recruitment module for BRCA1 at sites of DNA lesions.
Why Is BRCA1-A complex Important in Cell Biology?
The BRCA1-A complex is important because it provides the molecular link between K63-linked polyubiquitin signals at DNA damage sites and the recruitment of BRCA1, a critical tumor suppressor. Defects in this complex impair homologous recombination and lead to genomic instability, which underlies cancer predisposition and sensitivity to DNA-damaging agents. Moreover, the complex is a determinant of replication fork stability and repair pathway choice, making it a potential target for synthetic lethal strategies in ATM-deficient and BRCA1-A-deficient cancers.
• Central to BRCA1 recruitment at DNA double-strand breaks and stalled replication forks.
• Recognizes K63-linked polyubiquitin on histone H2A and H2AX, a specific epigenetic mark of DNA damage.
• BRCC3/BRCC36 deubiquitylase activity within the complex regulates its own assembly and function.
• Loss of BRCA1-A components causes homologous recombination deficiency and PARP inhibitor sensitivity.
• Restricts replication fork reversal-dependent repair in ATM-deficient cells, revealing a therapeutic vulnerability.
• Cooperates with LIG4 in extrachromosomal DNA biogenesis, contributing to drug resistance.
• Mutations in BRCA1-A subunits are associated with breast and ovarian cancer risk.
• Serves as a model for studying ubiquitin-dependent DNA damage signaling.
• Potential biomarker for predicting response to platinum and PARP inhibitors.
• Target for CRISPR screening to identify synthetic lethal interactions.
BRCA1-A complex
DNA Damage Recognition and K63-Ubiquitin Binding
In simple terms: The complex first finds the damaged spot by grabbing onto a specific tag on histones.
The BRCA1-A complex is recruited to DNA damage sites through the recognition of K63-linked polyubiquitin chains on histone H2A and H2AX. RAP80/UIMC1 contains ubiquitin-interacting motifs that bind these chains, while FAM175A/CCDC98/Abraxas and MERIT40/NBA1 stabilize the interaction and facilitate complex assembly. This recognition step is essential for the subsequent accumulation of BRCA1 at lesions.
Assembly of the BRCA1-BARD1 Heterodimer
In simple terms: The core enzyme of the complex, BRCA1 paired with BARD1, is brought together with the other subunits.
The BRCA1-A complex is built around the BRCA1-BARD1 heterodimer. BRCA1 interacts with BARD1 through its N-terminal RING domain, and this heterodimer is the catalytic and structural core of the complex. The other subunits, including RAP80, BRCC3, BRE, FAM175A, and MERIT40, assemble in a hierarchical manner to form the holo-complex. Disruption of any subunit can impair complex integrity and BRCA1 recruitment.
Deubiquitylation by BRCC3/BRCC36
In simple terms: One subunit acts as a molecular scissors that removes ubiquitin tags to fine-tune the complex's activity.
BRCC3/BRCC36 is a K63-specific deubiquitylase within the BRCA1-A complex. Its activity is regulated by autologous K63 deubiquitylation within the complex, which licenses DNA damage recognition and prevents premature disassembly. Structural and biochemical studies have revealed the mechanism of K63-linked polyubiquitin recognition and cleavage by the BRCA1-A complex, highlighting the importance of this enzymatic activity in DNA repair.
Role in Replication Fork Protection and Repair Pathway Choice
In simple terms: The complex also guards stalled replication forks and helps decide which repair pathway to use.
Beyond its canonical role in homologous recombination, the BRCA1-A complex restricts replication fork reversal-dependent DNA repair in ATM-deficient cells. This function is critical for maintaining fork stability and preventing excessive resection. Loss of BRCA1-A components in ATM-deficient backgrounds leads to synthetic lethality, suggesting that the complex is a key determinant of repair pathway choice under replication stress.
Cooperation with LIG4 in Extrachromosomal DNA Biogenesis
In simple terms: The complex also works with other repair factors to manage extra DNA circles that can cause drug resistance.
Recent evidence shows that BRCA1-A and LIG4 complexes mediate extrachromosomal DNA (ecDNA) biogenesis, a process that can drive oncogene amplification and drug resistance. This implicates the BRCA1-A complex in genome plasticity and cancer evolution, expanding its functional repertoire beyond canonical DNA repair.
Key Genes Involved in GO:0070531 BRCA1-A complex
The BRCA1-A complex comprises several core genes and proteins, each with distinct roles in complex assembly, DNA damage recognition, and enzymatic activity.
| Gene | Major Role | Research Relevance |
|---|---|---|
| BRCA1 | Core subunit; forms heterodimer with BARD1; essential for homologous recombination | Major breast/ovarian cancer susceptibility gene; target for PARP inhibitor therapy |
| BARD1 | Heterodimerization partner of BRCA1; stabilizes BRCA1 and contributes to E3 ligase activity | Mutations linked to cancer risk; required for complex integrity |
| RAP80/UIMC1 | Binds K63-linked polyubiquitin chains on H2A/H2AX; recruits BRCA1-A to damage sites | Key for damage recognition; loss impairs BRCA1 recruitment |
| BRCC3/BRCC36 | K63-specific deubiquitylase; regulates complex stability and function | Enzymatic activity critical for DNA damage recognition; target for inhibitor development |
| BRE/BRCC45 | Scaffold subunit; stabilizes complex and mediates interactions | Required for complex assembly and BRCA1 recruitment |
| FAM175A/CCDC98/Abraxas | Adaptor protein; links BRCA1 to RAP80 and other subunits | Mutations associated with cancer; essential for complex formation |
| MERIT40/NBA1 | Stabilizes complex; required for BRCA1 retention at damage sites | Loss leads to defective DNA repair and genomic instability |
| ATM | Kinase that regulates DNA damage response; interacts with BRCA1-A in fork protection | Synthetic lethal with BRCA1-A loss; therapeutic target |
| LIG4 | DNA ligase involved in non-homologous end joining; cooperates with BRCA1-A in ecDNA biogenesis | Linked to drug resistance and genome instability |
| EXO1 | Exonuclease involved in resection; potential therapeutic target in BRCA1-A deficient cancers | Synthetic lethal interactions with BRCA1-A loss |
| H2AX | Histone variant phosphorylated at damage sites; K63-ubiquitylated to recruit BRCA1-A | Epigenetic mark recognized by RAP80 |
| H2A | Histone substrate for K63-linked ubiquitylation at damage sites | Docking site for BRCA1-A complex |
| BRCC45 | Alternative name for BRE; part of the BRCA1-A complex | Scaffold function |
| CCDC98 | Alternative name for FAM175A; adaptor protein | Complex assembly |
| NBA1 | Alternative name for MERIT40; stabilizes complex | DNA repair efficiency |
| UIMC1 | Alternative name for RAP80; ubiquitin-binding subunit | Damage recognition |
| BRCC36 | Alternative name for BRCC3; deubiquitylase | Regulation of complex activity |
How Is BRCA1-A complex Regulated?
The BRCA1-A complex is regulated at multiple levels. Post-translational modification, particularly K63-linked ubiquitylation and deubiquitylation, controls its assembly and activity. Autologous K63 deubiquitylation by BRCC3/BRCC36 within the complex is required for DNA damage recognition and prevents premature disassembly. The complex also interacts with ATM signaling; in ATM-deficient cells, BRCA1-A restricts replication fork reversal-dependent repair, indicating that ATM status influences BRCA1-A function. Additionally, the complex is subject to cell cycle regulation, with its recruitment to damage sites occurring in a manner dependent on CDK activity. These regulatory mechanisms ensure that BRCA1-A acts at the right time and place to maintain genome stability.
BRCA1-A complex and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| BRCA1 | Hereditary breast and ovarian cancer; PARP inhibitor sensitivity | BRCA1 knockout cell lines (e.g., U2OS, HeLa) and patient-derived xenografts |
| BARD1 | Cancer predisposition; DNA repair deficiency | BARD1 knockout or point-mutant cell models |
| RAP80/UIMC1 | Defective DNA damage response; cancer risk | RAP80 knockout cells to study BRCA1 recruitment |
| BRCC3/BRCC36 | Impaired deubiquitylation; genomic instability | BRCC3 catalytic-dead knock-in models |
| FAM175A/CCDC98 | Cancer susceptibility; complex assembly defects | FAM175A knockout or truncating mutations |
BRCA1-A Complex and Hereditary Breast and Ovarian Cancer
Germline mutations in BRCA1 and its partner BARD1 are well-established causes of hereditary breast and ovarian cancer. The BRCA1-A complex is critical for BRCA1 function, and mutations in other subunits such as RAP80, FAM175A, and MERIT40 have been associated with increased cancer risk in some studies. Loss of BRCA1-A function leads to homologous recombination deficiency, which is the basis for the clinical use of PARP inhibitors in BRCA-mutant cancers.
Therapeutic Vulnerabilities in BRCA1-A Deficient Cancers
Cancers with defects in BRCA1-A components are sensitive to PARP inhibitors and platinum-based chemotherapy due to impaired homologous recombination. Recent studies have identified EXO1 as a therapeutic target in BRCA1-A complex deficient cancers, including those with Fanconi Anaemia and ZRSR2 mutations. Furthermore, BRCA1-A loss in ATM-deficient cells creates a synthetic lethal interaction that can be exploited with targeted therapies.
BRCA1-A Complex in Drug Resistance and Genome Evolution
The BRCA1-A complex, together with LIG4, mediates extrachromosomal DNA biogenesis, a process that can lead to oncogene amplification and resistance to targeted therapies. This suggests that BRCA1-A status may influence how tumors evolve under therapeutic pressure. Understanding these mechanisms could inform strategies to overcome drug resistance in cancers with BRCA1-A alterations.
From BRCA1-A complex-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the role of BRCA1-A in homologous recombination? | BRCA1 or BARD1 knockout cell lines complemented with wild-type or mutant constructs |
| How does BRCC3 deubiquitylase activity regulate complex function? | BRCC3 catalytic-dead point-mutant knock-in cells |
| Does RAP80 ubiquitin binding mediate BRCA1 recruitment? | RAP80 UIM point mutants or knockout cells |
| What are the synthetic lethal partners of BRCA1-A loss? | CRISPR knockout library screening in BRCA1-A-deficient backgrounds |
| How does BRCA1-A affect replication fork stability? | DNA fiber assays in BRCA1-A knockout cells treated with replication stress agents |
| Can BRCA1-A status predict drug resistance? | Patient-derived organoids with defined BRCA1-A mutations |
How to Study the BRCA1-A complex Process
| Method | What It Measures | Typical Application |
|---|---|---|
| CRISPR knockout screening | Gene essentiality and synthetic lethality | Identifying targets in BRCA1-A-deficient cancers |
| AP-MS proteomics | Protein-protein interactions and complex composition | Defining BRCA1-A subunits and assembly |
| Immunofluorescence foci analysis | Recruitment of BRCA1-A to DNA damage sites | Assessing mutations in RAP80 or BRCA1 |
| DNA fiber assay | Replication fork progression and reversal | Studying fork protection by BRCA1-A |
| Deubiquitylation assay | Enzymatic activity of BRCC3/BRCC36 | Testing catalytic mutants and inhibitors |
| CRISPR knock-in of tags | Endogenous protein localization and interactions | Live-cell imaging of BRCA1-A subunits |
| RNA-seq | Transcriptional changes upon BRCA1-A loss | Identifying pathways affected by complex deficiency |
| ecDNA detection (e.g., FISH) | Extrachromosomal DNA biogenesis | Linking BRCA1-A to drug resistance |
CRISPR-Based Genetic Screens
CRISPR knockout and activation screens are powerful tools to identify genes that are synthetic lethal with BRCA1-A components. For example, screens in BRCA1-A-deficient cells have revealed EXO1 as a therapeutic target. These screens can also uncover modifiers of PARP inhibitor sensitivity.
Proteomics and Interactomics
Affinity purification coupled with mass spectrometry (AP-MS) has been used to define the subunit composition of the BRCA1-A complex and its dynamic interactions. Proximity labeling approaches can capture transient interactions at DNA damage sites. These methods are essential for understanding how mutations affect complex assembly.
Imaging and DNA Damage Foci Analysis
Immunofluorescence microscopy of DNA damage foci, such as those containing BRCA1, RAP80, or phosphorylated H2AX, is a standard method to assess BRCA1-A recruitment. Live-cell imaging with fluorescently tagged subunits can reveal real-time dynamics at lesions.
Biochemical Assays for Deubiquitylation
In vitro deubiquitylation assays using K63-linked polyubiquitin chains and recombinant BRCC3/BRCC36 can measure enzymatic activity and the impact of mutations. These assays help dissect the mechanism of K63 linkage recognition and cleavage.
How CRISPR Can Be Used to Study GO:0070531 BRCA1-A complex
Knockout
CRISPR knockout of BRCA1-A subunits such as BRCA1, BARD1, RAP80, or BRCC3 is widely used to study loss-of-function phenotypes, including defective DNA repair, sensitivity to PARP inhibitors, and replication fork instability. These models are valuable for synthetic lethal screens and drug sensitivity testing.
Point Mutation
Point mutations can be introduced to dissect specific domains, such as the catalytic site of BRCC3/BRCC36 or the ubiquitin-interacting motifs of RAP80. For example, a catalytic-dead BRCC3 knock-in can reveal the importance of deubiquitylase activity in DNA damage recognition.
Knock-in
Knock-in of epitope tags or fluorescent proteins at endogenous loci allows for real-time imaging and biochemical isolation of the BRCA1-A complex. This approach preserves physiological expression levels and regulatory context, which is critical for studying dynamic assembly at damage sites.
Overexpression
Overexpression of wild-type or mutant BRCA1-A subunits can be used to test dominant-negative effects or to amplify complex formation for biochemical studies. However, careful controls are needed because overexpression may disrupt stoichiometry and lead to artifacts.
How EDITGENE Supports BRCA1-A complex Research
Researchers studying BRCA1-A complex-related genes often need to determine whether a candidate gene is causally involved in DNA repair, cancer predisposition, or drug response. This requires precise genetic models that can isolate the contribution of individual subunits and their domains. EDITGENE provides a comprehensive suite of CRISPR-based services to accelerate such investigations.
Contact EDITGENE today to design your custom CRISPR model for BRCA1-A complex research.
Related Products
| Product name | Cat.No. | Species | Gene ID | |
|---|---|---|---|---|
| UIMC1 Knockout HEK293 Cell Line | EDJ-KQ475 | Human | 51720 | Details Get a Quote |
| BABAM2 Knockout HEK293 Cell Line | EDJ-KQ3218 | Human | 9577 | Details Get a Quote |
| MPND Knockout HEK293 Cell Line | EDJ-KQ3815 | Human | 84954 | Details Get a Quote |
| ABRAXAS1 Knockout HEK293 Cell Line | EDJ-KQ9994 | Human | 84142 | Details Get a Quote |
| BRCC3 Knockout HEK293 Cell Line | EDJ-KQ11854 | Human | 79184 | Details Get a Quote |
| UIMC1 Knockout A-549 Cell Line | EDJ-KQ20119 | Human | 51720 | Details Get a Quote |
| UIMC1 Knockout HCT 116 Cell Line | EDJ-KQ20121 | Human | 51720 | Details Get a Quote |
| UIMC1 Knockout HeLa Cell Line | EDJ-KQ20122 | Human | 51720 | Details Get a Quote |
| MPND Knockout HCT 116 Cell Line | EDJ-KQ25942 | Human | 84954 | Details Get a Quote |
| MPND Knockout HeLa Cell Line | EDJ-KQ25943 | Human | 84954 | Details Get a Quote |
| ABRAXAS1 Knockout A-549 Cell Line | EDJ-KQ36947 | Human | 84142 | Details Get a Quote |
| ABRAXAS1 Knockout HCT 116 Cell Line | EDJ-KQ36948 | Human | 84142 | Details Get a Quote |
| ABRAXAS1 Knockout HeLa Cell Line | EDJ-KQ36949 | Human | 84142 | Details Get a Quote |
| MPND Knockout A-549 Cell Line | EDJ-KQ24584 | Human | 84954 | Details Get a Quote |
| BABAM2 Knockout A-549 Cell Line | EDJ-KQ24707 | Human | 9577 | Details Get a Quote |
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Frequently Asked Questions About BRCA1-A complex
What is the BRCA1-A complex?
The BRCA1-A complex is a protein assembly (GO:0070531) that contains BRCA1, BARD1, RAP80, BRCC3, BRE, FAM175A, and MERIT40, and binds K63-linked polyubiquitin on histone H2A/H2AX at DNA damage sites to recruit BRCA1.
What genes are involved in the BRCA1-A complex?
The core genes are BRCA1, BARD1, RAP80/UIMC1, BRCC3/BRCC36, BRE/BRCC45, FAM175A/CCDC98/Abraxas, and MERIT40/NBA1.
What is the function of GO:0070531?
GO:0070531 defines the cellular component that recognizes K63-linked polyubiquitin chains at DNA damage sites and facilitates BRCA1 recruitment for DNA repair.
How is the BRCA1-A complex regulated?
It is regulated by K63-linked ubiquitylation and deubiquitylation, particularly by BRCC3/BRCC36, and by ATM signaling and cell cycle-dependent phosphorylation.
What diseases are associated with BRCA1-A complex mutations?
Mutations in BRCA1-A components are linked to hereditary breast and ovarian cancer, PARP inhibitor sensitivity, and drug resistance.
What research methods are used to study the BRCA1-A complex?
Common methods include CRISPR knockout screens, AP-MS proteomics, immunofluorescence foci analysis, DNA fiber assays, and deubiquitylation assays.
How does BRCC3/BRCC36 contribute to BRCA1-A function?
BRCC3/BRCC36 is a K63-specific deubiquitylase that regulates complex stability and DNA damage recognition through autologous deubiquitylation.
Can BRCA1-A status predict response to PARP inhibitors?
Yes, loss of BRCA1-A function causes homologous recombination deficiency, which is associated with sensitivity to PARP inhibitors.
What is the role of RAP80 in the BRCA1-A complex?
RAP80/UIMC1 binds K63-linked polyubiquitin chains on histones and is essential for recruiting the complex to DNA damage sites.
How can CRISPR be used to study the BRCA1-A complex?
CRISPR knockout, point mutation, knock-in, and overexpression models allow precise dissection of subunit functions, complex assembly, and drug responses.
Conclusion
The BRCA1-A complex (GO:0070531) is a critical DNA damage response module that recognizes K63-linked polyubiquitin marks on histones and recruits BRCA1 to promote genome stability. Its dysfunction is directly linked to cancer predisposition and therapeutic vulnerabilities, making it a prime target for basic and translational research. Advances in CRISPR-based models and screening technologies continue to uncover new roles for this complex in replication fork protection, drug resistance, and genome evolution. Understanding the BRCA1-A complex in detail will inform the development of novel cancer therapies and precision medicine strategies.
References
- 1. Savage KI et al.. 2015. BRCA1, a 'complex' protein involved in the maintenance of genomic stability.. FEBS J 282(4):630-46 PMID: 25400280
- 2. Her J et al.. 2016. Factors forming the BRCA1-A complex orchestrate BRCA1 recruitment to the sites of DNA damage.. Acta Biochim Biophys Sin (Shanghai) 48(7):658-64 PMID: 27325824
- 3. Datta A et al.. 2026. The BRCA1-A complex restricts replication fork reversal-dependent DNA repair in ATM deficient cells.. Nat Commun 17(1) PMID: 42401588
- 4. Maric M et al.. 2025. EXO1 as a therapeutic target for Fanconi Anaemia, ZRSR2 and BRCA1-A complex deficient cancers.. Nat Commun 16(1):8476 PMID: 41006228
- 5. Jiang Q et al.. 2022. Autologous K63 deubiquitylation within the BRCA1-A complex licenses DNA damage recognition.. J Cell Biol 221(9) PMID: 35938958
- 6. Datta A et al.. 2026. The BRCA1-A complex restricts replication fork reversal-dependent DNA repair in ATM deficient cells.. bioRxiv PMID: 41889868
- 7. Foglizzo M et al.. 2026. Mechanism of K63-linked polyubiquitin recognition and cleavage by the BRCA1-A complex.. Nat Commun 17(1) PMID: 42581301
- 8. Chung OW et al.. 2026. BRCA1-A and LIG4 complexes mediate ecDNA biogenesis and cancer drug resistance.. Proc Natl Acad Sci U S A 123(11):e2530443123 PMID: 41811450
