GO:0031422 RecQ family helicase-topoisomerase III complex: Components, Assembly and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0031422 describes a conserved complex containing a RecQ family helicase and a topoisomerase III homologue (type IA subfamily), which may include additional proteins.
• The complex acts as a DNA structure-specific dissolvasome, resolving recombination intermediates such as double Holliday junctions.
• It is conserved from E. coli to human, with core components including RecQ helicases (e.g., BLM, WRN, RECQL4) and topoisomerase III alpha (TOP3A).
• Dysfunction of this complex is linked to genome instability and human diseases such as Bloom syndrome, Werner syndrome, and Rothmund-Thomson syndrome.
• Studying this complex requires integrated approaches including CRISPR knockout, knock-in, and biochemical assays.
• EDITGENE provides custom cell models and screening services to dissect the function of this complex in health and disease.
Description
The RecQ family helicase-topoisomerase III complex (GO:0031422) is a cellular component that plays a central role in maintaining genome stability. It is defined as a complex containing a RecQ family helicase and a topoisomerase III homologue, which may also include additional proteins, and is conserved from E. coli to human. This complex is often referred to as the RecQ helicase-Topo III complex or the Sgs1-Top3 complex in yeast. Researchers study this complex because it resolves DNA recombination intermediates that, if left unresolved, can lead to chromosomal rearrangements and cell death. The complex is a key player in the dissolution of double Holliday junctions, a process that prevents crossing over and maintains genomic integrity. Understanding its structure, assembly, and regulation is essential for uncovering mechanisms of cancer and premature aging disorders.
RecQ family helicase-topoisomerase III complex At A Glance
| GO ID | GO:0031422 |
|---|---|
| GO term | RecQ family helicase-topoisomerase III complex |
| Ontology | cellular_component |
| Synonym | RecQ helicase-Topo III complex; Sgs1-Top3 complex |
| Major function | DNA structure-specific dissolution of recombination intermediates, including double Holliday junctions |
| Conservation | Conserved from E. coli to human |
| Core components | RecQ family helicase (e.g., BLM, WRN, RECQL4) and topoisomerase III homologue (e.g., TOP3A) |
| Additional proteins | May include RMI1, RMI2, and other accessory factors |
| Associated diseases | Bloom syndrome, Werner syndrome, Rothmund-Thomson syndrome, cancer predisposition |
What Is GO:0031422?
GO:0031422 is a Gene Ontology cellular component term that defines a protein complex composed of a RecQ family helicase and a topoisomerase III homologue (a member of the topoisomerase type IA subfamily). The complex may also contain one or more additional proteins and is evolutionarily conserved from E. coli to human. Synonyms include RecQ helicase-Topo III complex and Sgs1-Top3 complex.
Why Is RecQ family helicase-topoisomerase III complex Important in Cell Biology?
The RecQ family helicase-topoisomerase III complex is critical for genome maintenance because it resolves DNA recombination intermediates that would otherwise cause chromosomal instability. Defects in this complex are directly linked to human genetic disorders characterized by cancer predisposition and premature aging, making it a prime target for therapeutic intervention and basic research.
• Maintains genome stability by dissolving double Holliday junctions and preventing sister chromatid exchange.
• Mutations in complex components cause Bloom syndrome, Werner syndrome, and Rothmund-Thomson syndrome.
• Plays a role in DNA replication, repair, and recombination pathways.
• Loss of function leads to increased mutation rates and chromosomal rearrangements.
• Serves as a model for understanding conserved DNA transaction mechanisms from bacteria to humans.
• Potential target for cancer therapy, as cancer cells with defective homologous recombination may rely on this complex.
• Involved in telomere maintenance and aging processes.
• Provides a paradigm for studying protein-protein interactions in DNA metabolism.
What Happens During RecQ family helicase-topoisomerase III complex?
Recognition of DNA recombination intermediates
In simple terms: The complex first finds and binds to tangled DNA structures that form during recombination.
The RecQ helicase component recognizes and binds to specific DNA structures such as double Holliday junctions, which are intermediates in homologous recombination. This binding is structure-specific and is the first step in the dissolution process.
Helicase-driven branch migration
In simple terms: The helicase part of the complex unwinds and moves the DNA branches to bring them together.
Once bound, the RecQ helicase uses ATP hydrolysis to drive branch migration, moving the crossover point along the DNA and remodeling the junction into a conformation suitable for resolution.
Topoisomerase III-mediated strand passage
In simple terms: The topoisomerase enzyme cuts and rejoins DNA strands to allow them to pass through each other.
The topoisomerase III homologue catalyzes transient single-strand breaks and strand passage, which resolves the intertwined DNA strands. This activity is essential for the final dissolution of the recombination intermediate.
Dissolution of double Holliday junctions
In simple terms: The complex completes the process by separating the DNA strands without leaving breaks or crossovers.
The coordinated action of the helicase and topoisomerase leads to the dissolution of double Holliday junctions into non-crossover products, thereby preventing loss of heterozygosity and maintaining genomic integrity.
Key Genes Involved in GO:0031422 RecQ family helicase-topoisomerase III complex
The following genes encode components and accessory factors of the RecQ family helicase-topoisomerase III complex across species.
| Gene | Major Role | Research Relevance |
|---|---|---|
| BLM | RecQ helicase in humans; drives branch migration and dissolution | Mutations cause Bloom syndrome; model for cancer and genome instability |
| WRN | RecQ helicase in humans; involved in replication and repair | Mutations cause Werner syndrome; studied in aging and cancer |
| RECQL4 | RecQ helicase in humans; roles in replication and repair | Mutations cause Rothmund-Thomson syndrome; linked to osteosarcoma |
| TOP3A | Topoisomerase III alpha; resolves DNA strands | Essential for dissolution; mutations linked to Bloom syndrome-like disorder |
| RMI1 | Accessory protein; stimulates complex activity | Required for efficient dissolution; knockout leads to genome instability |
| RMI2 | Accessory protein; stabilizes complex | Mutations cause Bloom syndrome-like phenotype |
| SGS1 | Yeast RecQ helicase; ortholog of BLM | Model for studying complex function in Saccharomyces cerevisiae |
| TOP3 | Yeast topoisomerase III; ortholog of TOP3A | Essential for dissolution in yeast; genetic studies |
| RMI1 (yeast) | Yeast accessory protein | Required for Sgs1-Top3 function |
| RECQ1 | Human RecQ helicase; may interact with TOP3A | Implicated in cancer and DNA repair |
| RECQL5 | Human RecQ helicase; roles in transcription and replication | Potential tumor suppressor; studied in cancer |
| E. coli RecQ | Bacterial RecQ helicase; model for RecQ family | Biochemical studies of helicase mechanism |
| E. coli TopB | Bacterial topoisomerase III; partner of RecQ | Model for complex assembly and function |
| Drosophila Blm | RecQ helicase in flies; involved in genome stability | Genetic model for Bloom syndrome |
| C. elegans HIM-6 | RecQ helicase; involved in meiosis | Model for recombination and genome stability |
| Arabidopsis RECQ4A | Plant RecQ helicase; roles in recombination | Model for plant genome stability |
| Human TOP3B | Topoisomerase III beta; may form complex with RecQ helicases | Linked to neurological disorders |
| Human RMI1 | Accessory protein; part of dissolvasome | Biochemical and structural studies |
How Is RecQ family helicase-topoisomerase III complex Regulated?
The activity of the RecQ family helicase-topoisomerase III complex is regulated by post-translational modifications and protein-protein interactions. For example, sumoylation of BLM and TOP3A modulates complex assembly and dissolution activity. Additionally, the complex is regulated by cell cycle-dependent phosphorylation, which influences its recruitment to sites of DNA damage. Accessory proteins such as RMI1 and RMI2 are essential for stabilizing the complex and stimulating its catalytic activity.
RecQ family helicase-topoisomerase III complex and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| BLM | Bloom syndrome; cancer predisposition | BLM knockout cell lines; patient-derived fibroblasts |
| WRN | Werner syndrome; premature aging | WRN knockout human stem cells; mouse models |
| RECQL4 | Rothmund-Thomson syndrome; osteosarcoma | RECQL4 knockout cells; zebrafish models |
| TOP3A | Bloom syndrome-like disorder; genome instability | TOP3A knockout cells; conditional mouse models |
| RMI1 | Bloom syndrome-like phenotype; genome instability | RMI1 knockout cells; yeast models |
Bloom syndrome
Bloom syndrome is caused by mutations in the BLM gene, which encodes a RecQ helicase that partners with TOP3A in the RecQ family helicase-topoisomerase III complex. Loss of BLM function leads to defective dissolution of double Holliday junctions, resulting in elevated sister chromatid exchange, chromosomal instability, and increased cancer predisposition.
Werner syndrome
Werner syndrome is a premature aging disorder caused by mutations in WRN, another RecQ helicase. Although WRN may not form a stable complex with TOP3A in all contexts, it shares functional overlap with the RecQ-topoisomerase III complex in resolving recombination intermediates. Defects in WRN lead to genomic instability and accelerated aging.
Rothmund-Thomson syndrome
Rothmund-Thomson syndrome is associated with mutations in RECQL4, a RecQ helicase that may interact with topoisomerase III. This syndrome is characterized by skin abnormalities, skeletal defects, and increased risk of osteosarcoma. The role of RECQL4 in the RecQ-topoisomerase III complex is an area of active research.
Cancer predisposition
Defects in the RecQ family helicase-topoisomerase III complex lead to genome instability, which is a hallmark of cancer. Cells from Bloom syndrome patients exhibit high rates of loss of heterozygosity and chromosomal rearrangements, predisposing them to various malignancies. Targeting this complex is being explored as a therapeutic strategy in cancers with homologous recombination defects.
From RecQ family helicase-topoisomerase III complex-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the role of BLM in complex assembly? | BLM knockout cell line (e.g., HeLa or HCT116) |
| How does TOP3A mutation affect dissolution activity? | TOP3A point-mutant knock-in cells |
| Can we visualize complex formation in live cells? | Endogenous BLM-fluorescent tag knock-in cells |
| What are the interaction partners of the complex? | Overexpression of tagged BLM and TOP3A followed by proteomics |
| Does loss of RMI1 cause genome instability? | RMI1 knockout cells and yeast mutants |
| How does the complex respond to DNA damage? | CRISPR knockout of BLM with DNA damage agents |
How to Study the RecQ family helicase-topoisomerase III complex Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Electrophoretic mobility shift assay (EMSA) | DNA binding affinity of the complex | Studying structure-specific recognition |
| ATPase assay | Helicase activity | Measuring energy consumption during branch migration |
| Topoisomerase assay | Strand passage activity | Assessing topoisomerase III function |
| CRISPR knockout | Loss-of-function phenotypes | Determining gene essentiality and genome stability |
| CRISPR knock-in | Tagged protein expression | Live-cell imaging and proteomics |
| Mass spectrometry | Protein-protein interactions | Identifying novel complex components |
| Fluorescence microscopy | Subcellular localization | Visualizing complex at DNA damage sites |
| Yeast genetics | Genetic interactions | Modeling complex function in S. cerevisiae |
Biochemical reconstitution
Purified RecQ helicase and topoisomerase III can be combined in vitro to study complex assembly and dissolution activity on synthetic DNA substrates. This method allows precise control of components and conditions.
CRISPR-based genome editing
Knockout, knock-in, and point mutations of genes encoding complex components (e.g., BLM, TOP3A) enable functional studies in cells. These models help determine the contribution of each subunit to genome stability.
Proteomics and interactomics
Affinity purification coupled with mass spectrometry can identify additional proteins that associate with the RecQ-topoisomerase III complex, revealing its dynamic composition and regulation.
Imaging and live-cell assays
Fluorescent tagging of complex components allows visualization of their localization and dynamics at sites of DNA damage or during replication. This provides spatial and temporal insights into complex function.
How CRISPR Can Be Used to Study GO:0031422 RecQ family helicase-topoisomerase III complex
Knockout
CRISPR knockout of genes encoding RecQ helicases (e.g., BLM) or topoisomerase III (e.g., TOP3A) creates cell lines that lack the complex. These models are used to study the consequences of complex loss, such as increased sister chromatid exchange, sensitivity to DNA-damaging agents, and genome instability.
Point Mutation
Introducing specific point mutations into the helicase or topoisomerase domains via CRISPR allows researchers to dissect catalytic activities without completely abolishing protein expression. For example, helicase-dead mutants can separate the roles of ATP hydrolysis from protein-protein interactions.
Knock-in
Knock-in of epitope tags or fluorescent proteins at endogenous loci enables visualization and purification of the complex from cells. This approach preserves native regulation and stoichiometry, providing insights into complex assembly and dynamics.
Overexpression
Overexpression of wild-type or mutant complex components can be achieved by CRISPR-mediated insertion of strong promoters or by lentiviral transduction. This is useful for biochemical purification and for studying dominant-negative effects.
How EDITGENE Supports RecQ family helicase-topoisomerase III complex Research
Researchers studying RecQ family helicase-topoisomerase III complex-related genes often need to determine whether a candidate gene is causally involved in genome stability, disease, or drug response. EDITGENE provides a comprehensive suite of CRISPR services to create precisely engineered cell models, enabling rigorous functional studies of this complex.
Contact EDITGENE today to design your custom CRISPR model for RecQ family helicase-topoisomerase III complex research.
Frequently Asked Questions About RecQ family helicase-topoisomerase III complex
What is GO:0031422?
GO:0031422 is a Gene Ontology cellular component term that defines the RecQ family helicase-topoisomerase III complex, a conserved protein complex involved in DNA recombination intermediate dissolution.
What genes are involved in the RecQ family helicase-topoisomerase III complex?
Key genes include BLM, WRN, RECQL4, TOP3A, RMI1, and RMI2 in humans, as well as SGS1 and TOP3 in yeast.
What is the function of the RecQ helicase-topoisomerase III complex?
It resolves double Holliday junctions and other recombination intermediates through a dissolvasome activity, preventing chromosomal instability.
Which diseases are associated with defects in this complex?
Mutations in complex components cause Bloom syndrome, Werner syndrome, Rothmund-Thomson syndrome, and increase cancer predisposition.
How is the RecQ family helicase-topoisomerase III complex regulated?
It is regulated by post-translational modifications such as sumoylation and phosphorylation, as well as by accessory proteins like RMI1 and RMI2.
What model systems are used to study this complex?
Common models include human cell lines with CRISPR knockouts, yeast Saccharomyces cerevisiae, and purified proteins for biochemical assays.
What is the role of BLM in the complex?
BLM is a RecQ helicase that drives branch migration and is essential for the dissolution of double Holliday junctions.
How does TOP3A contribute to complex function?
TOP3A is a topoisomerase III alpha that catalyzes strand passage, resolving the DNA strands during dissolution.
Can CRISPR be used to study this complex?
Yes, CRISPR knockout, knock-in, and point mutation models are powerful tools to dissect the function of each component.
What services does EDITGENE offer for studying this complex?
EDITGENE provides knockout, point mutation, knock-in, overexpression cell models, CRISPR library screening, and bioinformatics services.
Conclusion
The RecQ family helicase-topoisomerase III complex (GO:0031422) is a conserved molecular machine essential for genome stability. Its ability to dissolve recombination intermediates protects cells from chromosomal rearrangements and cancer. Understanding its structure, regulation, and disease links requires advanced experimental models. EDITGENE offers a comprehensive toolkit to accelerate research on this complex, from gene editing to functional screening.
References
- 1. Mankouri HW et al.. 2007. The RecQ helicase-topoisomerase III-Rmi1 complex: a DNA structure-specific 'dissolvasome'?. Trends Biochem Sci 32(12):538-46 PMID: 17980605
