GO:0070533 BRCA1-C complex: Components, Assembly and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0070533 (BRCA1-C complex) is a cellular_component defined as a protein complex containing the BRCA1-BARD1 heterodimer, CtIP and the Mre11/Rad50/NBS1 (M/R/N) complex that binds DNA at damage sites.
• BRCA1-C binding to damaged DNA is required for DNA damage-induced Chk1 phosphorylation and the G2/M transition checkpoint.
• The complex is functionally distinct from BRCA1-A and BRCA1-B complexes, which orchestrate BRCA1 recruitment and other repair steps.
• BRCA1-C drives DNA end resection and protects DNA ends, a central step in homologous recombination repair.
• ABRAXAS1 (Abraxas) and related adaptors orchestrate BRCA1 activities and help counter genome-destabilizing repair pathways.
• Dysregulation of BRCA1-C components is linked to breast and ovarian cancer predisposition and to radiotherapy/chemotherapy responses.
Description
The BRCA1-C complex (GO:0070533) is a DNA damage-responsive protein assembly that contains the BRCA1-BARD1 heterodimer, CtIP, and the Mre11/Rad50/NBS1 (M/R/N) complex, and binds to DNA at sites of damage. It is one of several distinct BRCA1-containing complexes, alongside BRCA1-A and BRCA1-B, that partition BRCA1 functions across the DNA damage response. Because BRCA1-C binding to damaged DNA is required for DNA damage-induced Chk1 phosphorylation and the G2/M transition checkpoint, the complex sits at the interface of DNA repair and cell-cycle control. For researchers, GO:0070533 provides a precise annotation target for dissecting how BRCA1-containing assemblies are built, how they are recruited to lesions, and how they signal to checkpoint kinases. Functional studies of BRCA1-C components have clarified mechanisms of DNA end resection and DNA protection, which are central to homologous recombination and to the response to radiotherapy and DNA-damaging chemotherapy. Variants in BRCA1 and its partners continue to be reclassified using complex functional assays, making the BRCA1-C complex a practical framework for interpreting variants of uncertain significance and for designing mechanism-based experiments.
BRCA1-C complex At A Glance
| GO ID | GO:0070533 |
|---|---|
| GO term | BRCA1-C complex |
| Ontology | cellular_component |
| Synonym | None listed in QuickGO |
| Major function | Binds DNA at DNA damage sites; required for DNA damage-induced Chk1 phosphorylation and the G2/M transition checkpoint |
| Core components | BRCA1-BARD1 heterodimer, CtIP, and the Mre11/Rad50/NBS1 (M/R/N) complex |
| Related complexes | BRCA1-A and BRCA1-B complexes, which orchestrate BRCA1 recruitment and other repair functions |
| Process context | DNA damage response, DNA end resection, DNA protection, and cell-cycle checkpoint signaling |
| Disease relevance | Breast and ovarian cancer predisposition and therapy response |
What Is GO:0070533?
In our own words, GO:0070533 describes a specific nuclear protein complex that includes the BRCA1-BARD1 heterodimer, CtIP, and the Mre11/Rad50/NBS1 (M/R/N) complex. This assembly binds to DNA at sites of DNA damage, and this binding is required for DNA damage-induced Chk1 phosphorylation and for the G2/M transition checkpoint. The term is a cellular_component annotation, meaning it classifies where a gene product acts rather than a catalytic activity or a standalone pathway.
Why Is BRCA1-C complex Important in Cell Biology?
The BRCA1-C complex matters because it couples the physical detection of DNA damage to checkpoint signaling and repair. Its DNA-binding step is required for Chk1 phosphorylation and the G2/M transition checkpoint, which determines whether damaged cells arrest or proceed. At the same time, BRCA1-C components participate in DNA end resection and DNA protection, the decisive steps that channel lesions into homologous recombination. Because BRCA1-A, BRCA1-B, and BRCA1-C complexes have distinct compositions and functions, resolving which complex acts in a given context is essential for interpreting BRCA1 biology and for understanding how cancer-associated variants perturb repair.
• Defines a specific BRCA1-containing assembly distinct from BRCA1-A and BRCA1-B complexes.
• Links DNA damage recognition to Chk1 phosphorylation and the G2/M transition checkpoint.
• Provides a mechanistic framework for DNA end resection and DNA protection during homologous recombination.
• Helps explain how BRCA1 adaptors such as ABRAXAS1 orchestrate BRCA1 activities against genome-destabilizing repair pathways.
• Supports functional reclassification of BRCA1/2 variants of uncertain significance.
• Informs radiotherapy sensitization strategies that target DNA damage response signaling.
• Offers a cellular_component annotation for interpreting proteomic and imaging data on BRCA1 assemblies.
• Connects to breast and ovarian cancer biology through BRCA1 pathway dysfunction.
Structure and Composition of BRCA1-C complex
BRCA1-BARD1 heterodimer as the core scaffold
In simple terms: BRCA1 and BARD1 pair up to form the central building block of the complex.
The BRCA1-C complex contains the BRCA1-BARD1 heterodimer, which serves as a core scaffold that organizes the assembly and its DNA-binding behavior. BRCA1-BARD1 function is directly implicated in DNA end resection and DNA protection, making the heterodimer a mechanistic hub of the complex.
CtIP as a resection-promoting partner
In simple terms: CtIP is a partner protein that helps prepare DNA ends for repair.
CtIP is listed as a component of the BRCA1-C complex together with the BRCA1-BARD1 heterodimer and the M/R/N complex. Its inclusion places the complex at the initiation of DNA end resection, the step that commits lesions to homologous recombination.
Mre11/Rad50/NBS1 (M/R/N) complex
In simple terms: The M/R/N complex is the DNA-end sensing and processing module.
The Mre11/Rad50/NBS1 (M/R/N) complex is a defined component of BRCA1-C, and its presence links the assembly to DNA damage detection and end processing. Together with BRCA1-BARD1 and CtIP, M/R/N supports the resection and protection activities attributed to the complex.
DNA binding at damage sites
In simple terms: The complex must physically bind damaged DNA to do its job.
BRCA1-C binds to DNA at DNA damage sites, and this binding is required for DNA damage-induced Chk1 phosphorylation and the G2/M transition checkpoint. This DNA-binding requirement distinguishes the complex functionally from other BRCA1-containing assemblies.
Distinction from BRCA1-A and BRCA1-B complexes
In simple terms: BRCA1 forms several different complexes, and BRCA1-C is only one of them.
Systematic investigation of BRCA1-A, BRCA1-B, and BRCA1-C complexes shows that they have distinct compositions and functions in DNA damage response and DNA repair. Factors forming the BRCA1-A complex orchestrate BRCA1 recruitment to damage sites, illustrating how different BRCA1 complexes partition tasks.
Key Genes Involved in GO:0070533 BRCA1-C complex
The following genes and proteins are the experimentally defined components and functional partners of the BRCA1-C complex and its related BRCA1 assemblies.
| Gene | Major Role | Research Relevance |
|---|---|---|
| BRCA1 | Core scaffold of the BRCA1-BARD1 heterodimer in BRCA1-C | Central to DNA end resection, DNA protection, and checkpoint signaling |
| BARD1 | Heterodimerization partner of BRCA1 in BRCA1-C | Required for BRCA1-BARD1 function in resection and protection |
| CtIP | Component of BRCA1-C that supports DNA end resection | Links BRCA1-C to commitment to homologous recombination |
| MRE11 | Subunit of the Mre11/Rad50/NBS1 (M/R/N) complex in BRCA1-C | DNA-end sensing and processing within the complex |
| RAD50 | Subunit of the Mre11/Rad50/NBS1 (M/R/N) complex in BRCA1-C | Structural and processing role in DNA damage detection |
| NBS1 | Subunit of the Mre11/Rad50/NBS1 (M/R/N) complex in BRCA1-C | Connects the complex to DNA damage signaling |
| ABRAXAS1 | Orchestrates BRCA1 activities and counters genome-destabilizing repair pathways | Breast cancer patient-derived insights into BRCA1 regulation |
| CHEK1 | Chk1 kinase whose phosphorylation depends on BRCA1-C DNA binding | Readout of BRCA1-C-dependent checkpoint activation |
| ATM | Upstream DNA damage kinase in the response pathway | Context for BRCA1 complex regulation after irradiation |
| ABL1 | c-Abl kinase that associates with BRCA1 and is disrupted after irradiation | Illustrates ATM-dependent regulation of BRCA1 complexes |
| BRCA2 | Homologous recombination factor in the broader BRCA pathway | Comparator for BRCA1-C-specific functions |
| PALB2 | Homologous recombination partner in BRCA-related repair | Context for interpreting BRCA1-C pathway dependencies |
| RAD51 | Recombinase downstream of resection | Functional readout of successful resection and repair |
| TP53BP1 | DNA damage response factor influencing repair pathway choice | Helps interpret BRCA1-C-dependent repair decisions |
| RFC | Processivity factor with non-catalytic roles in PCNA-mediated DNA synthesis | Context for DNA synthesis steps adjacent to repair |
| PCNA | Sliding clamp for processive DNA synthesis | Relevant to DNA synthesis steps in damage response |
How Is BRCA1-C complex Regulated?
BRCA1-C function is embedded in the DNA damage response signaling network. DNA damage-induced Chk1 phosphorylation and the G2/M transition checkpoint require BRCA1-C binding to damaged DNA, placing the complex under the control of upstream damage signals. ATM-dependent signaling regulates BRCA1 complexes; constitutive association of BRCA1 and c-Abl is disrupted after irradiation in an ATM-dependent manner, illustrating how damage signals remodel BRCA1-containing assemblies. ABRAXAS1 further orchestrates BRCA1 activities to counter genome-destabilizing repair pathways, providing an adaptor-level layer of regulation. Systematic comparison of BRCA1-A, BRCA1-B, and BRCA1-C complexes indicates that their distinct compositions underlie their distinct regulatory roles in DNA damage response and DNA repair.
BRCA1-C complex and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| BRCA1 | Breast and ovarian cancer predisposition; DNA repair deficiency | Knockout and point-mutation cell models for variant reclassification |
| ABRAXAS1 | Breast cancer and genome destabilization | Knockout models to test BRCA1 activity orchestration |
| CHEK1 | Checkpoint signaling and radiotherapy response | Phospho-Chk1 readout models after DNA damage |
| MRE11 | DNA damage response and repair pathway choice | Knockout models to assess resection and protection |
| BARD1 | BRCA1-dependent repair and cancer risk | Heterodimerization and functional assays in cell models |
Breast and ovarian cancer predisposition
BRCA1 pathway dysfunction is a well-established contributor to breast and ovarian cancer predisposition, and functional studies of BRCA1/2 variants of uncertain significance help clarify which changes are pathogenic. ABRAXAS1, a regulator of BRCA1 activities, has been studied in breast cancer patients to understand how disrupted BRCA1 regulation destabilizes the genome. Because BRCA1-C is a defined BRCA1-containing complex, its components are candidate contributors to inherited cancer risk.
Radiotherapy and chemotherapy response
DNA damage response signaling pathways, including those involving BRCA1 complexes, are targets for radiotherapy sensitization in cancer. The requirement of BRCA1-C DNA binding for Chk1 phosphorylation and the G2/M checkpoint suggests that complex status can influence how tumor cells respond to DNA-damaging treatment. Understanding BRCA1-C composition and function therefore supports rational design of combination strategies that exploit repair defects.
Genome instability and repair pathway choice
BRCA1-C components participate in DNA end resection and DNA protection, processes that determine repair pathway choice and genome stability. ABRAXAS1 counters genome-destabilizing repair pathways, reinforcing the idea that BRCA1 regulation is a barrier against inappropriate repair. Systematic analysis of BRCA1-A, BRCA1-B, and BRCA1-C complexes further supports the view that mispartitioning of BRCA1 functions contributes to genome instability.
From BRCA1-C complex-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of BRCA1-C component X impair Chk1 phosphorylation after damage? | Knockout cell model with phospho-Chk1 readout |
| Does a BRCA1 variant of uncertain significance disrupt complex function? | Point-mutation knock-in model for functional reclassification |
| Where does BRCA1-C assemble after DNA damage? | Tagged knock-in for imaging and localization |
| Does overexpression of a component alter resection or protection? | Overexpression cell model with resection assays |
| How do BRCA1-A, BRCA1-B, and BRCA1-C complexes differ functionally? | Parallel knockout and tagged knock-in panels |
| Does ABRAXAS1 loss destabilize the genome? | Knockout model with genome stability assays |
How to Study the BRCA1-C complex Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Phospho-Chk1 immunoblotting | DNA damage-induced Chk1 phosphorylation | Testing BRCA1-C-dependent checkpoint activation |
| Cell-cycle profiling | G2/M transition checkpoint integrity | Assessing checkpoint function after damage |
| DNA end resection assays | Single-stranded DNA formation and end processing | Evaluating BRCA1-BARD1 resection and protection |
| Co-immunoprecipitation / proteomics | Complex composition and interactions | Mapping BRCA1-A, -B, and -C membership |
| Imaging of tagged components | Localization at DNA damage sites | Visualizing BRCA1-C assembly |
| Variant functional assays | Impact of variants on complex function | Reclassifying variants of uncertain significance |
| Genome stability assays | Accumulation of genome destabilization | Testing ABRAXAS1 and BRCA1 pathway defects |
| DNA synthesis assays | Processive DNA synthesis and PCNA-dependent steps | Contextualizing repair-associated synthesis |
DNA damage and checkpoint assays
Because BRCA1-C DNA binding is required for DNA damage-induced Chk1 phosphorylation and the G2/M transition checkpoint, phospho-Chk1 measurement and cell-cycle analysis after induced damage are direct functional readouts. These assays can be combined with irradiation or DNA-damaging agents to probe pathway activity.
Resection and DNA protection assays
BRCA1-BARD1 function in DNA end resection and DNA protection can be interrogated with resection-specific assays that monitor single-stranded DNA formation and end processing. Such assays help distinguish BRCA1-C-dependent functions from other BRCA1 complex activities.
Complex composition and interaction analysis
Systematic investigation of BRCA1-A, BRCA1-B, and BRCA1-C complexes relies on biochemical and proteomic approaches to define composition and interactions. Factors forming the BRCA1-A complex were identified through analysis of BRCA1 recruitment to damage sites, illustrating how interaction studies map complex membership.
Variant functional studies
Complex functional studies have been used to reclassify BRCA1/2 variants of uncertain significance, integrating multiple assays to infer pathogenicity. Applying similar logic to BRCA1-C components can clarify whether a variant perturbs complex assembly or activity.
How CRISPR Can Be Used to Study GO:0070533 BRCA1-C complex
Knockout
CRISPR knockout of BRCA1-C components such as BRCA1, BARD1, CtIP, MRE11, RAD50, or NBS1 can be used to test requirements for Chk1 phosphorylation and the G2/M checkpoint after DNA damage. Knockout of ABRAXAS1 provides a way to probe how BRCA1 activities are orchestrated against genome-destabilizing repair pathways. Parallel knockout panels help distinguish BRCA1-A, BRCA1-B, and BRCA1-C functions.
Point Mutation
Point-mutation models are suited to interrogating specific residues implicated in BRCA1-C assembly or DNA binding, especially when variants of uncertain significance are identified. Such models allow functional reclassification by testing whether a defined amino acid change disrupts complex-dependent readouts. They also help separate DNA-binding defects from other functions of the complex.
Knock-in
Tagged knock-in of BRCA1-C components enables visualization and biochemical isolation of the complex at DNA damage sites. Knock-in of disease-associated variants allows study of their effects in a native genomic context, complementing overexpression systems. These models are valuable for tracking assembly and localization in real time.
Overexpression
Overexpression of BRCA1-C components can be used to test whether increased dosage alters DNA end resection, DNA protection, or checkpoint signaling. Overexpression models are also useful for producing material for interaction and structural studies of the complex. Careful controls are needed because stoichiometry affects BRCA1 complex behavior.
How EDITGENE Supports BRCA1-C complex Research
Researchers studying BRCA1-C complex-related genes often need to determine whether a candidate gene is causally involved in DNA damage response, checkpoint signaling, or repair pathway choice, and whether a specific variant alters complex function. EDITGENE provides CRISPR-based cell model services that let teams move from correlation to causation with defined genetic edits.
Contact EDITGENE today to design your custom CRISPR model for BRCA1-C complex research.
Frequently Asked Questions About BRCA1-C complex
What is the BRCA1-C complex (GO:0070533)?
It is a cellular_component defined as a protein complex that contains the BRCA1-BARD1 heterodimer, CtIP, and the Mre11/Rad50/NBS1 (M/R/N) complex, and binds to DNA at DNA damage sites.
What genes are involved in the BRCA1-C complex?
Core components include BRCA1, BARD1, CtIP, MRE11, RAD50, and NBS1, with ABRAXAS1 acting as a regulator of BRCA1 activities.
What does BRCA1-C binding to damaged DNA do?
BRCA1-C binding to damaged DNA is required for DNA damage-induced Chk1 phosphorylation and the G2/M transition checkpoint.
How is BRCA1-C different from BRCA1-A and BRCA1-B complexes?
Systematic investigation shows that BRCA1-A, BRCA1-B, and BRCA1-C complexes have distinct compositions and functions in DNA damage response and DNA repair.
What is the role of BRCA1-BARD1 in the BRCA1-C complex?
The BRCA1-BARD1 heterodimer is a core component and functions in DNA end resection and DNA protection.
Why is the Mre11/Rad50/NBS1 complex part of BRCA1-C?
The M/R/N complex is a defined component of BRCA1-C and contributes DNA damage detection and end processing activities.
Is the BRCA1-C complex linked to cancer?
BRCA1 pathway dysfunction is linked to breast and ovarian cancer predisposition, and functional studies help reclassify BRCA1/2 variants of uncertain significance.
How do researchers study the BRCA1-C complex?
Common approaches include phospho-Chk1 assays, cell-cycle profiling, DNA end resection assays, co-immunoprecipitation, proteomics, and imaging of tagged components.
Can CRISPR be used to study BRCA1-C complex genes?
Yes, knockout, point-mutation, knock-in, and overexpression models can test requirements for checkpoint signaling, resection, and genome stability.
What readouts indicate BRCA1-C activity?
DNA damage-induced Chk1 phosphorylation and G2/M checkpoint integrity are direct readouts, complemented by resection and DNA protection assays.
Conclusion
GO:0070533 (BRCA1-C complex) defines a specific BRCA1-containing assembly built from the BRCA1-BARD1 heterodimer, CtIP, and the Mre11/Rad50/NBS1 complex that binds DNA at damage sites and is required for Chk1 phosphorylation and the G2/M transition checkpoint. Its distinction from BRCA1-A and BRCA1-B complexes makes it a precise annotation for dissecting how BRCA1 functions are partitioned during the DNA damage response. Because BRCA1-C components intersect with DNA end resection, DNA protection, genome stability, and cancer predisposition, they are compelling targets for functional variant studies and for CRISPR-based causal experiments. Well-designed knockout, point-mutation, knock-in, and overexpression models, combined with checkpoint and resection readouts, provide a practical route to mechanistic insight.
References
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- 3. Sachsenweger J et al.. 2023. ABRAXAS1 orchestrates BRCA1 activities to counter genome destabilizing repair pathways-lessons from breast cancer patients.. Cell Death Dis 14(5):328 PMID: 37198153
- 4. 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
- 5. Li S et al.. 2024. Systematic investigation of BRCA1-A, -B, and -C complexes and their functions in DNA damage response and DNA repair.. Oncogene 43(35):2621-2634 PMID: 39068216
- 6. Chua GNL et al.. 2026. A non-catalytic role for RFC in PCNA-mediated processive DNA synthesis.. Cell 189(4):1124-1134.e14 PMID: 41610851
- 7. Foray N et al.. 2002. Constitutive association of BRCA1 and c-Abl and its ATM-dependent disruption after irradiation.. Mol Cell Biol 22(12):4020-32 PMID: 12024016
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