GO:0070532 BRCA1-B complex: Components, Assembly and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0070532 (BRCA1-B complex) is a cellular_component term describing a protein complex that contains the BRCA1-BARD1 heterodimer, BACH1 and TopBP1, and binds to DNA during S phase at DNA damage sites.
• The BRCA1-B complex is one of several BRCA1-containing complexes; its assembly and recruitment to DNA damage sites are orchestrated by factors that also form the BRCA1-A complex.
• BRCA1 recruitment to sites of DNA damage is a critical step in DNA repair and genome maintenance, and defects in this process are linked to cancer predisposition.
• Researchers study the BRCA1-B complex using knockout, point-mutation, knock-in and overexpression cell models, combined with imaging, proteomics and functional assays.
• Understanding the BRCA1-B complex helps explain how cells maintain genomic stability and why BRCA1 mutations lead to breast and ovarian cancer.
• EDITGENE provides CRISPR-based services to model BRCA1-B complex components for mechanistic and translational research.
Description
The BRCA1-B complex (GO:0070532) is a cellular_component defined as a protein complex that contains the BRCA1-BARD1 heterodimer, BACH1 and TopBP1, and binds to DNA during S phase at DNA damage sites. This complex is part of the broader machinery that recruits BRCA1 to sites of DNA damage, a process essential for genome maintenance. The BRCA1-B complex is distinguished from other BRCA1-containing complexes by its specific subunit composition and its role during S phase. Researchers study this complex to understand how cells respond to DNA damage and how defects in this response contribute to cancer. The BRCA1-B complex is one of several complexes formed by BRCA1, and its assembly is coordinated with factors that also form the BRCA1-A complex. Because BRCA1 is a major tumor suppressor, understanding the BRCA1-B complex has direct implications for cancer biology and therapeutic development.
BRCA1-B complex At A Glance
| GO ID | GO:0070532 |
|---|---|
| GO term | BRCA1-B complex |
| Ontology | cellular_component |
| Synonym | None |
| Major function | Binds to DNA during S phase at DNA damage sites; contains BRCA1-BARD1 heterodimer, BACH1 and TopBP1 |
| Subunits | BRCA1, BARD1, BACH1, TopBP1 |
| Cell cycle phase | S phase |
| Localization | DNA damage sites |
| Related complex | BRCA1-A complex; factors forming BRCA1-A also orchestrate BRCA1 recruitment |
What Is GO:0070532?
The BRCA1-B complex is a protein complex that contains the BRCA1-BARD1 heterodimer, BACH1 and TopBP1, and binds to DNA during S phase at DNA damage sites. This definition, from the Gene Ontology, places the complex in the cellular_component ontology and highlights its role in DNA damage response during DNA replication.
Why Is BRCA1-B complex Important in Cell Biology?
The BRCA1-B complex is important because it is a key player in the recruitment of BRCA1 to DNA damage sites during S phase, a process that is essential for maintaining genomic stability. Defects in BRCA1 recruitment and function are associated with increased risk of breast and ovarian cancer, making the BRCA1-B complex a subject of intense research. Understanding how this complex assembles and functions can inform the development of targeted therapies and diagnostic tools.
• The BRCA1-B complex is critical for BRCA1 recruitment to DNA damage sites during S phase.
• It contains the BRCA1-BARD1 heterodimer, a central tumor suppressor module.
• Its assembly is coordinated with factors that also form the BRCA1-A complex.
• Defects in BRCA1 recruitment are linked to cancer predisposition.
• Studying the BRCA1-B complex helps elucidate DNA damage response mechanisms.
• It provides a target for understanding chemotherapy and PARP inhibitor responses.
• The complex is relevant to breast and ovarian cancer research.
• It serves as a model for studying protein complex assembly at DNA lesions.
• Understanding its structure can guide drug design.
• It is a focus for CRISPR-based functional genomics.
What Happens During BRCA1-B complex?
Recruitment to DNA damage sites
In simple terms: The BRCA1-B complex is called to the scene when DNA is damaged during DNA copying.
The BRCA1-B complex binds to DNA during S phase at DNA damage sites. This recruitment is orchestrated by factors that also form the BRCA1-A complex, which help localize BRCA1 to lesions.
Assembly of the BRCA1-BARD1 heterodimer
In simple terms: BRCA1 pairs with BARD1 to form the core of the complex.
The complex contains the BRCA1-BARD1 heterodimer, which is a key functional unit. This heterodimer is essential for the complex's ability to bind DNA and participate in damage response.
Interaction with BACH1 and TopBP1
In simple terms: Two other proteins, BACH1 and TopBP1, join the complex to help it work.
BACH1 and TopBP1 are integral components of the BRCA1-B complex. Their presence distinguishes this complex from other BRCA1-containing complexes and contributes to its specific functions during S phase.
Coordination with BRCA1-A complex factors
In simple terms: The same helper proteins that build the BRCA1-A complex also help build the BRCA1-B complex.
Factors forming the BRCA1-A complex orchestrate BRCA1 recruitment to sites of DNA damage. This suggests a shared regulatory mechanism for different BRCA1 complexes.
Key Genes Involved in GO:0070532 BRCA1-B complex
The BRCA1-B complex comprises several key genes and proteins that are central to its function and regulation.
| Gene | Major Role | Research Relevance |
|---|---|---|
| BRCA1 | Core subunit; forms heterodimer with BARD1; tumor suppressor | Mutations linked to breast/ovarian cancer; target for functional studies |
| BARD1 | Forms heterodimer with BRCA1; essential for complex stability | Partner of BRCA1; mutations also associated with cancer risk |
| BACH1 | Component of BRCA1-B complex; contributes to DNA damage response | Distinguishes BRCA1-B from other complexes; potential biomarker |
| TopBP1 | Component of BRCA1-B complex; involved in DNA replication and damage response | Links complex to S phase and replication stress |
| BRCA1-A complex factors | Orchestrate BRCA1 recruitment to DNA damage sites | Shared assembly machinery; targets for understanding recruitment |
| BRCA2 | Related DNA repair protein; not a subunit but functionally linked | Context for BRCA1-B function in homologous recombination |
| PALB2 | BRCA2 partner; involved in BRCA1 recruitment pathways | Potential modifier of BRCA1-B complex function |
| RAD51 | Downstream effector of homologous recombination | Readout of BRCA1-B complex activity |
| ATM | DNA damage sensor kinase; upstream of BRCA1 recruitment | Regulates damage response pathways |
| ATR | DNA damage sensor kinase; activated during S phase | Coordinates replication stress responses |
| CHEK1 | Effector kinase downstream of ATR | Cell cycle checkpoint control |
| CHEK2 | Effector kinase downstream of ATM | DNA damage signaling |
| H2AX | Histone variant phosphorylated at damage sites | Marker of DNA damage foci |
| MDC1 | Mediator of DNA damage response | Recruits BRCA1 complexes |
| RNF8 | Ubiquitin ligase in damage response | Upstream of BRCA1 recruitment |
| RNF168 | Ubiquitin ligase in damage response | Upstream of BRCA1 recruitment |
| 53BP1 | DNA damage response protein; influences repair pathway choice | Antagonizes BRCA1-mediated resection |
| CtIP | Promotes DNA end resection | Functional interplay with BRCA1 |
How Is BRCA1-B complex Regulated?
The BRCA1-B complex is regulated by factors that also form the BRCA1-A complex, which orchestrate BRCA1 recruitment to sites of DNA damage. This shared regulatory mechanism ensures proper localization of BRCA1 during S phase. Additionally, upstream kinases such as ATM and ATR are likely involved in signaling to the complex, though specific details require further study.
BRCA1-B complex and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| BRCA1 | Breast and ovarian cancer; DNA repair deficiency | BRCA1 knockout cell lines; point mutations in RING domain |
| BARD1 | Cancer predisposition; DNA damage response | BARD1 knockout and knock-in models |
| BACH1 | Cancer; DNA damage response | BACH1 knockout cells; overexpression studies |
| TopBP1 | Cancer; replication stress | TopBP1 knockout and tagged knock-in |
| BRCA1-A complex factors | Cancer; BRCA1 recruitment defects | Knockout of shared assembly factors |
Breast and ovarian cancer
Mutations in BRCA1, a core component of the BRCA1-B complex, are strongly associated with increased risk of breast and ovarian cancer. Defects in BRCA1 recruitment to DNA damage sites, a process involving the BRCA1-B complex, contribute to genomic instability and tumorigenesis.
Other cancers
Alterations in BRCA1-B complex components such as BARD1, BACH1 and TopBP1 have been implicated in various cancers, though the exact mechanisms are still being elucidated. The complex's role in DNA repair makes it a potential target for cancer therapy.
Therapeutic implications
Understanding the BRCA1-B complex can inform the use of PARP inhibitors and other DNA-damaging agents in cancer treatment. Cells with defective BRCA1-B complex function may be sensitive to specific therapies.
From BRCA1-B complex-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of BRCA1-B complex component impair DNA damage repair? | Knockout cell lines for BRCA1, BARD1, BACH1 or TopBP1 |
| How do point mutations in BRCA1 affect complex assembly? | Point-mutation knock-in models |
| Where does the complex localize during S phase? | Tagged knock-in with fluorescent proteins |
| Can overexpression of BACH1 rescue complex function? | Overexpression cell models |
| What are the interaction partners of the complex? | Affinity purification proteomics from tagged knock-in cells |
| Does the complex influence sensitivity to PARP inhibitors? | Knockout and point-mutation models treated with drugs |
How to Study the BRCA1-B complex Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Immunofluorescence | Localization of complex components at DNA damage sites | Assessing recruitment during S phase |
| Co-immunoprecipitation | Protein-protein interactions within the complex | Validating subunit composition |
| Mass spectrometry | Identification of complex subunits and interactors | Defining the BRCA1-B interactome |
| Comet assay | DNA damage and repair capacity | Functional impact of complex loss |
| HR reporter assay | Homologous recombination efficiency | Measuring repair pathway activity |
| CRISPR knockout screening | Genes affecting complex function or drug sensitivity | Identifying modifiers and synthetic lethal partners |
| Live-cell imaging | Real-time recruitment dynamics | Studying S phase-specific binding |
| Western blot | Protein expression and modification | Validating knockout or overexpression |
Imaging of DNA damage foci
Immunofluorescence and live-cell imaging can visualize recruitment of BRCA1-B complex components to DNA damage sites marked by H2AX phosphorylation. This method reveals spatial and temporal dynamics during S phase.
Proteomics and interactomics
Affinity purification coupled with mass spectrometry can identify subunits and interactors of the BRCA1-B complex. This helps define the complex composition and its regulation.
Functional assays for DNA repair
Comet assays, homologous recombination reporters and sensitivity to DNA-damaging agents measure the functional impact of BRCA1-B complex perturbations.
CRISPR screening
Genome-wide CRISPR knockout screens can identify genes that modify BRCA1-B complex function or synthetic lethality with its components.
How CRISPR Can Be Used to Study GO:0070532 BRCA1-B complex
Knockout
CRISPR knockout of BRCA1, BARD1, BACH1 or TopBP1 can abolish BRCA1-B complex formation and impair DNA damage repair. These models are useful for studying loss-of-function phenotypes and drug sensitivity.
Point Mutation
Point mutations in BRCA1 or BARD1 can be introduced to mimic cancer-associated missense variants and assess their impact on complex assembly and function.
Knock-in
Knock-in of tagged versions of complex components allows for visualization and affinity purification without altering endogenous regulation.
Overexpression
Overexpression of individual subunits or the entire complex can be used to study gain-of-function effects and rescue experiments.
How EDITGENE Supports BRCA1-B complex Research
Researchers studying BRCA1-B complex-related genes often need to determine whether a candidate gene is causally involved in complex assembly, DNA damage response, or cancer predisposition. EDITGENE provides a comprehensive suite of CRISPR services to create precisely engineered cell models for such investigations.
Contact EDITGENE today to design your custom CRISPR model for BRCA1-B complex research.
Frequently Asked Questions About BRCA1-B complex
What is the BRCA1-B complex?
The BRCA1-B complex (GO:0070532) is a protein complex that contains the BRCA1-BARD1 heterodimer, BACH1 and TopBP1, and binds to DNA during S phase at DNA damage sites.
What genes are involved in the BRCA1-B complex?
The main genes are BRCA1, BARD1, BACH1 and TopBP1.
Where is the BRCA1-B complex located?
It localizes to DNA damage sites during S phase.
What is the function of the BRCA1-B complex?
It binds to DNA at damage sites and is involved in DNA damage response and genome maintenance.
How is the BRCA1-B complex regulated?
Its assembly and recruitment are orchestrated by factors that also form the BRCA1-A complex.
What diseases are associated with the BRCA1-B complex?
Defects in its components, especially BRCA1, are linked to breast and ovarian cancer.
How can I study the BRCA1-B complex?
Using CRISPR knockout, point mutation, knock-in and overexpression models, combined with imaging and proteomics.
What is the difference between BRCA1-A and BRCA1-B complexes?
They share some assembly factors but have distinct subunit compositions; BRCA1-B contains BACH1 and TopBP1.
Can I order custom cell models for BRCA1-B complex research?
Yes, EDITGENE provides CRISPR services to generate such models.
What methods are used to analyze the BRCA1-B complex?
Immunofluorescence, co-immunoprecipitation, mass spectrometry, comet assay, HR reporter assays and CRISPR screens.
Conclusion
The BRCA1-B complex (GO:0070532) is a key protein assembly that binds to DNA during S phase at damage sites and is essential for BRCA1 recruitment and genome stability. Its components, including BRCA1, BARD1, BACH1 and TopBP1, are critical for DNA damage response and are implicated in cancer. Studying this complex using CRISPR-based models can reveal new insights into cancer biology and therapeutic strategies.
References
- 1. 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
