GO:0030915 Smc5-Smc6 complex: Components, Assembly and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0030915 (Smc5-Smc6 complex) is a conserved cellular component built around an Smc5p-Smc6p heterodimer plus non-SMC subunits, and it functions in DNA repair and in maintaining cell cycle arrest after DNA damage.
• The complex is best characterized in Saccharomyces cerevisiae as the octameric Mms21-Smc5-Smc6 complex, with at least five subunits conserved in fission yeast and humans.
• Smc5-Smc6 helps suppress gross chromosomal rearrangements, preserve nucleolar integrity, and resolve chromosome junctions in meiosis.
• Recent work shows the SMC5/SMC6 complex is critical for resolving R-loop-induced transcription-replication conflicts.
• Smc5-Smc6 acts within the broader family of SMC complexes that control genome organization and chromosome dynamics.
• Drosophila studies link the Smc5/Smc6/MAGE complex to resistance to caffeine and genotoxic stress, highlighting conserved stress-response roles.
Description
The Smc5-Smc6 complex (GO:0030915) is a conserved cellular component that contains a heterodimer of SMC proteins, Smc5p and Smc6p, together with several non-SMC subunits, and it is involved in DNA repair and in maintaining cell cycle arrest following DNA damage. In Saccharomyces cerevisiae, this is an octameric complex called the Mms21-Smc5-Smc6 complex, with at least five of its subunits conserved in fission yeast and humans. Because the complex sits at the intersection of chromosome organization, replication, and repair, it is a recurring focus for researchers studying genome stability. Functionally, the Smc5-Smc6 complex is not a single-enzyme machine but a structural and regulatory hub. It contributes to suppressing gross chromosomal rearrangements mediated by break-induced replication, preserves nucleolar integrity in S. cerevisiae, and is required to remove chromosome junctions in meiosis. More recently, the SMC5/SMC6 complex has been shown to be critical for resolving R-loop-induced transcription-replication conflicts, linking it directly to co-transcriptional genome instability. For biomedical researchers, GO:0030915 is therefore both a mechanistic entry point and a practical target for perturbation studies. The complex is conserved across model organisms, from budding yeast to Drosophila and humans, which makes it tractable for knockout, point-mutation, knock-in, and overexpression experiments in multiple systems. Understanding its composition and regulation is essential for interpreting DNA-damage phenotypes and for designing CRISPR-based models of genome instability.
Smc5-Smc6 complex At A Glance
| GO ID | GO:0030915 |
|---|---|
| GO term | Smc5-Smc6 complex |
| Ontology | cellular_component |
| Synonym | None listed |
| Major function | DNA repair and maintenance of cell cycle arrest following DNA damage |
| Core architecture | Heterodimer of SMC proteins Smc5p and Smc6p plus several non-SMC proteins |
| Model-system name | Mms21-Smc5-Smc6 complex (octameric) in S. cerevisiae |
| Conservation | At least five subunits conserved in fission yeast and humans |
| Related processes | Suppression of break-induced replication rearrangements, nucleolar integrity, meiotic chromosome junction removal, R-loop resolution |
What Is GO:0030915?
GO:0030915 describes the Smc5-Smc6 complex: a conserved protein complex that contains a heterodimer of SMC proteins (Smc5p and Smc6p, or their homologs) and several additional proteins. It participates in DNA repair and in maintaining cell cycle arrest after DNA damage. In S. cerevisiae, the complex is octameric and is known as the Mms21-Smc5-Smc6 complex, and at least five of its subunits are conserved in fission yeast and humans.
Why Is Smc5-Smc6 complex Important in Cell Biology?
The Smc5-Smc6 complex matters because it is a conserved guardian of genome stability that couples chromosome organization to DNA repair and cell cycle control. Its dysfunction is associated with gross chromosomal rearrangements, nucleolar disruption, defective meiotic chromosome resolution, and transcription-replication conflicts, all of which are hallmarks of genome instability relevant to cancer and developmental disease. Because the complex is conserved from yeast to humans, findings in model organisms can be translated into mechanistic hypotheses for human cells, making GO:0030915 a high-value annotation for functional genomics and CRISPR screening.
• Defines a conserved SMC-based machine required for DNA repair and damage-induced cell cycle arrest.
• Suppresses gross chromosomal rearrangements mediated by break-induced replication.
• Preserves nucleolar integrity in S. cerevisiae, linking it to ribosome biogenesis and nuclear organization.
• Is required to remove chromosome junctions in meiosis, connecting it to fertility and germline stability.
• Resolves R-loop-induced transcription-replication conflicts, a major source of endogenous DNA damage.
• Belongs to the broader SMC complex family that controls genome organization and chromosome dynamics.
• Confers resistance to caffeine and genotoxic stress in Drosophila, indicating conserved stress-response functions.
• Provides a tractable target for CRISPR knockout, point-mutation, knock-in, and overexpression studies across model organisms.
Smc5-Smc6 complex: Biological Process, Structure, and Molecular Mechanism
What Happens During Smc5-Smc6 complex?
In simple terms: The complex acts as a repair and checkpoint coordinator when DNA is damaged.
The Smc5-Smc6 complex is involved in DNA repair and in maintaining cell cycle arrest following DNA damage. In budding yeast, it preserves nucleolar integrity, indicating a role in protecting specialized nuclear subdomains from damage-induced disruption. It also suppresses gross chromosomal rearrangements that arise through break-induced replication, a homology-directed repair pathway that can cause rearrangements when misregulated. In meiosis, the complex is required to remove chromosome junctions, a step needed for proper chromosome segregation. More recently, the SMC5/SMC6 complex was shown to be critical for resolving R-loop-induced transcription-replication conflicts, linking its repair function to co-transcriptional RNA-DNA hybrid management.
Structure and Composition of Smc5-Smc6 complex
In simple terms: The complex is built from two large SMC proteins plus several smaller partner proteins.
GO:0030915 is defined as a complex containing a heterodimer of SMC proteins, Smc5p and Smc6p, and several other proteins. In S. cerevisiae, the complex is octameric and is called the Mms21-Smc5-Smc6 complex, and at least five of its subunits are conserved in fission yeast and humans. The non-SMC subunits include kleisin and non-kleisin components that bridge the Smc5-Smc6 heads, as described for the Smc5-Smc6 DNA repair complex. This architecture places the complex within the broader family of SMC complexes that control genome organization.
Molecular Mechanism of Smc5-Smc6 complex
In simple terms: The complex uses its SMC arms and bridging subunits to hold and process DNA during repair.
The Smc5-Smc6 DNA repair complex bridges the Smc5-Smc6 heads via kleisin, Nse4, and non-kleisin subunits, forming a ring-like structure that can topologically engage DNA. This architecture is characteristic of SMC complexes, which control genome organization through ATP-dependent DNA loop extrusion and related mechanisms. The complex functions in DNA repair and in maintaining cell cycle arrest after damage, implying coordination with checkpoint signaling. Its ability to resolve R-loop-induced transcription-replication conflicts suggests it acts on RNA-DNA hybrid-containing structures that block replication.
Regulation and Checkpoint Integration
In simple terms: The complex is switched on or recruited when cells detect DNA damage.
The Smc5-Smc6 complex is involved in maintaining cell cycle arrest following DNA damage, which places it downstream of or in parallel with DNA damage checkpoint signaling. Its role in suppressing break-induced replication rearrangements implies that its activity must be tightly controlled to avoid inappropriate recombination. In Drosophila, the Smc5/Smc6/MAGE complex confers resistance to caffeine and genotoxic stress, indicating that its regulation is conserved and stress-responsive. The complex also preserves nucleolar integrity, suggesting that its regulation is coupled to nuclear organization and ribosome biogenesis.
Conservation Across Model Organisms
In simple terms: The same basic complex is found in yeast, flies, and humans.
The Smc5-Smc6 complex is conserved, with at least five subunits conserved in fission yeast and humans. In Drosophila melanogaster, the Smc5/Smc6/MAGE complex confers resistance to caffeine and genotoxic stress, demonstrating functional conservation in metazoans. The complex belongs to the SMC family that controls genome organization across eukaryotes. This conservation makes yeast and fly models valuable for dissecting mechanisms that are likely relevant to human cells.
Key Genes Involved in GO:0030915 Smc5-Smc6 complex
The following genes and proteins are core components or conserved partners of the Smc5-Smc6 complex (GO:0030915), based on the QuickGO definition and verified literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| SMC5 | SMC protein subunit; forms heterodimer with SMC6 | Core structural component of GO:0030915; knockout causes DNA repair defects |
| SMC6 | SMC protein subunit; forms heterodimer with SMC5 | Core structural component; essential for complex stability and function |
| MMS21 | Non-SMC subunit of the octameric Mms21-Smc5-Smc6 complex | Defines the S. cerevisiae octameric complex name |
| NSE4 | Kleisin subunit that bridges Smc5-Smc6 heads | Required for complex architecture and DNA bridging |
| NSE1 | Non-kleisin subunit of the Smc5-Smc6 complex | Contributes to complex integrity and repair function |
| NSE3 | Non-kleisin subunit of the Smc5-Smc6 complex | Contributes to complex integrity and repair function |
| NSE5 | Non-SMC subunit conserved in fission yeast and humans | Conserved component; useful for cross-species studies |
| NSE6 | Non-SMC subunit conserved in fission yeast and humans | Conserved component; useful for cross-species studies |
| MAGE | Partner in Drosophila Smc5/Smc6/MAGE complex | Confers resistance to caffeine and genotoxic stress |
| SMC5/SMC6 (human) | Human homologs of yeast Smc5p/Smc6p | Relevant to human genome stability and disease models |
| NSE1-NSE4 (human) | Human homologs of yeast non-SMC subunits | Conserved subunits for human cell CRISPR studies |
| NSE5-NSE6 (human) | Human homologs of yeast non-SMC subunits | Conserved subunits for human cell CRISPR studies |
| SMC5/SMC6 (fission yeast) | Fission yeast homologs | Model for conserved subunit function |
| SMC5/SMC6 (Drosophila) | Fly homologs in Smc5/Smc6/MAGE complex | Model for genotoxic stress resistance |
| Mms21 (S. cerevisiae) | SUMO ligase subunit of the complex | Links complex to SUMOylation and repair |
| Kleisin subunit | Bridges Smc5-Smc6 heads | Essential for ring architecture |
| Non-kleisin subunits | Accessory proteins in the complex | Required for DNA repair function |
How Is Smc5-Smc6 complex Regulated?
The Smc5-Smc6 complex is regulated in the context of the DNA damage response, as it is involved in maintaining cell cycle arrest following DNA damage. Its activity is also linked to the resolution of R-loop-induced transcription-replication conflicts, implying regulation by transcription and replication stress. In Drosophila, the Smc5/Smc6/MAGE complex confers resistance to caffeine and genotoxic stress, indicating stress-responsive regulation. The complex preserves nucleolar integrity, suggesting regulation coupled to nuclear organization. No specific upstream kinase or SUMO pathway is detailed in the provided verified citations beyond the general DNA damage response context.
Smc5-Smc6 complex and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| SMC5 | Genome instability, cancer predisposition | CRISPR knockout in human cell lines |
| SMC6 | Genome instability, cancer predisposition | CRISPR knockout in human cell lines |
| NSE4 | DNA repair deficiency | Point-mutation knock-in in yeast or human cells |
| MMS21 | Defective SUMOylation and DNA repair | Knockout in S. cerevisiae |
| MAGE | Genotoxic stress sensitivity | Drosophila knockout or overexpression |
Genome Instability and Cancer
The Smc5-Smc6 complex suppresses gross chromosomal rearrangements mediated by break-induced replication, a type of genome instability that can drive oncogenic rearrangements. Its role in resolving R-loop-induced transcription-replication conflicts further links it to endogenous sources of DNA damage that contribute to cancer-associated mutations. Because the complex is conserved in humans, loss-of-function alterations in SMC5/SMC6 or their partners could contribute to genome instability syndromes and tumorigenesis.
Meiotic Defects and Infertility
The Smc5-Smc6 complex is required to remove chromosome junctions in meiosis, a process essential for proper chromosome segregation and gamete formation. Defects in this function could lead to meiotic arrest, aneuploidy, or infertility, making the complex relevant to reproductive biology.
Nucleolar Stress and Ribosome Biogenesis
Smc5-Smc6 preserves nucleolar integrity in S. cerevisiae, connecting the complex to ribosome biogenesis and nucleolar stress responses. Disruption of nucleolar integrity is observed in various diseases, including cancer and ribosomopathies, suggesting that Smc5-Smc6 dysfunction could contribute to these conditions.
Genotoxic Stress Response
In Drosophila melanogaster, the Smc5/Smc6/MAGE complex confers resistance to caffeine and genotoxic stress, indicating a conserved role in protecting cells from DNA-damaging agents. This has implications for understanding chemoresistance and for developing sensitizers that target DNA repair pathways.
From Smc5-Smc6 complex-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of SMC5/SMC6 cause DNA repair defects? | CRISPR knockout in human cell lines or yeast |
| Does a specific point mutation in NSE4 disrupt complex assembly? | Point-mutation knock-in in S. cerevisiae |
| Can tagged SMC5 rescue genome instability? | Tagged knock-in of SMC5 in human cells |
| Does overexpression of SMC6 suppress R-loop-induced damage? | Overexpression in human cell lines |
| Is the MAGE subunit required for genotoxic stress resistance? | Drosophila knockout or overexpression |
| Does Smc5-Smc6 loss affect meiotic chromosome segregation? | Yeast meiosis knockout models |
How to Study the Smc5-Smc6 complex Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Gross chromosomal rearrangement assay | Frequency of chromosomal rearrangements | Testing Smc5-Smc6 suppression of break-induced replication |
| DRIP-seq / R-loop IP | R-loop accumulation | Assessing transcription-replication conflicts |
| Meiotic chromosome spreads | Chromosome junction resolution | Studying meiosis defects |
| Fluorescence microscopy | Nucleolar integrity | Testing nucleolar stress |
| CRISPR knockout screening | Gene essentiality and DNA repair defects | Identifying Smc5-Smc6 pathway dependencies |
| Co-immunoprecipitation | Protein-protein interactions | Mapping complex composition |
| Yeast genetics | Genetic interactions and synthetic phenotypes | Dissecting subunit functions |
| Drosophila stress assays | Genotoxic stress resistance | Testing MAGE subunit function |
Genomic Instability Assays
Gross chromosomal rearrangement assays in yeast can measure the role of Smc5-Smc6 in suppressing break-induced replication rearrangements. These assays are typically combined with CRISPR knockout of SMC5, SMC6, or non-SMC subunits to test causality.
R-Loop and Transcription-Replication Conflict Detection
R-loop detection methods, such as DRIP-seq or R-loop immunoprecipitation, can assess whether SMC5/SMC6 loss increases R-loop accumulation and transcription-replication conflicts. These experiments are often performed in human cell lines with CRISPR knockout or knockdown of SMC5/SMC6.
Meiotic Chromosome Analysis
Meiotic chromosome spreads and junction-resolution assays in yeast can determine whether Smc5-Smc6 is required for removing chromosome junctions during meiosis. Knockout or point-mutation models are used to dissect specific subunit requirements.
Nucleolar Integrity Imaging
Fluorescence microscopy of nucleolar markers can assess whether Smc5-Smc6 loss disrupts nucleolar integrity in S. cerevisiae. This approach can be combined with DNA damage agents to test stress responses.
How CRISPR Can Be Used to Study GO:0030915 Smc5-Smc6 complex
Knockout
CRISPR knockout of SMC5, SMC6, or non-SMC subunit genes can be used to test their requirement for DNA repair, cell cycle arrest, and genome stability. Knockout models in yeast and human cells are valuable for dissecting conserved functions.
Point Mutation
Point-mutation knock-in can be used to disrupt specific domains, such as the kleisin or non-kleisin bridging interfaces, to test their role in complex assembly and DNA repair. These models help separate structural from catalytic functions.
Knock-in
Tagged knock-in of SMC5 or SMC6 allows visualization and immunoprecipitation of the complex in its endogenous context. This is useful for mapping localization and interaction partners.
Overexpression
Overexpression of SMC5/SMC6 or partner subunits can test whether increased complex levels suppress R-loop-induced damage or genotoxic stress. Overexpression models are also useful for structure-function studies.
How EDITGENE Supports Smc5-Smc6 complex Research
Researchers studying Smc5-Smc6 complex-related genes often need to determine whether a candidate gene is causally involved in DNA repair, genome stability, or stress resistance. EDITGENE provides CRISPR-based cell models and screening services to accelerate this work.
Contact EDITGENE today to design your custom CRISPR model for Smc5-Smc6 complex research.
Frequently Asked Questions About Smc5-Smc6 complex
What is the Smc5-Smc6 complex?
The Smc5-Smc6 complex (GO:0030915) is a conserved cellular component containing an Smc5p-Smc6p heterodimer and several other proteins, involved in DNA repair and maintaining cell cycle arrest after DNA damage.
What genes are involved in the Smc5-Smc6 complex?
Core genes include SMC5, SMC6, MMS21, NSE1, NSE3, NSE4, NSE5, and NSE6, with at least five subunits conserved in fission yeast and humans.
What is the function of GO:0030915?
GO:0030915 functions in DNA repair and in maintaining cell cycle arrest following DNA damage, and it helps suppress gross chromosomal rearrangements.
Where is the Smc5-Smc6 complex found?
It is found in eukaryotes from yeast to humans, with the octameric Mms21-Smc5-Smc6 complex characterized in S. cerevisiae.
How does Smc5-Smc6 resolve R-loops?
The SMC5/SMC6 complex is critical for resolving R-loop-induced transcription-replication conflicts, which are sources of endogenous DNA damage.
Is Smc5-Smc6 involved in meiosis?
Yes, the Smc5-Smc6 complex is required to remove chromosome junctions in meiosis.
What diseases are linked to Smc5-Smc6 dysfunction?
Dysfunction is linked to genome instability, cancer predisposition, meiotic defects, and nucleolar stress.
How can I study Smc5-Smc6 with CRISPR?
CRISPR knockout, point-mutation knock-in, tagged knock-in, and overexpression models can be used to dissect subunit functions and genome stability phenotypes.
What model organisms are used for Smc5-Smc6 research?
S. cerevisiae, fission yeast, Drosophila melanogaster, and human cell lines are commonly used.
What is the Mms21-Smc5-Smc6 complex?
It is the octameric form of the Smc5-Smc6 complex in S. cerevisiae, named after its Mms21 subunit.
Conclusion
The Smc5-Smc6 complex (GO:0030915) is a conserved SMC-based machine that safeguards genome stability through DNA repair, checkpoint maintenance, and resolution of transcription-replication conflicts. Its roles in nucleolar integrity, meiosis, and genotoxic stress resistance make it relevant to cancer, infertility, and genome instability research. CRISPR-based models from EDITGENE can accelerate functional dissection of this complex across model systems.
References
- 1. De Piccoli G et al.. 2009. The unnamed complex: what do we know about Smc5-Smc6?. Chromosome Res 17(2):251-63 PMID: 19308705
- 2. Wu T et al.. 2026. The SMC5/SMC6 complex is critical for resolving R-loop-induced transcription-replication conflicts.. Nucleic Acids Res 54(2) PMID: 41533569
- 3. Hoencamp C et al.. 2023. Genome control by SMC complexes.. Nat Rev Mol Cell Biol 24(9):633-650 PMID: 37231112
- 4. Li X et al.. 2013. The Smc5/Smc6/MAGE complex confers resistance to caffeine and genotoxic stress in Drosophila melanogaster.. PLoS One 8(3):e59866 PMID: 23555814
- 5. Hwang JY et al.. 2008. Smc5-Smc6 complex suppresses gross chromosomal rearrangements mediated by break-induced replications.. DNA Repair (Amst) 7(9):1426-36 PMID: 18585101
- 6. Torres-Rosell J et al.. 2005. Smc5-Smc6 complex preserves nucleolar integrity in S. cerevisiae.. Cell Cycle 4(7):868-72 PMID: 15917663
- 7. Farmer S et al.. 2011. The Smc5-Smc6 complex is required to remove chromosome junctions in meiosis.. PLoS One 6(6):e20948 PMID: 21731634
- 8. Palecek J et al.. 2006. The Smc5-Smc6 DNA repair complex. bridging of the Smc5-Smc6 heads by the KLEISIN, Nse4, and non-Kleisin subunits.. J Biol Chem 281(48):36952-9 PMID: 17005570
