GO:0003916 DNA topoisomerase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0003916 DNA topoisomerase activity describes the catalysis of transient cleavage and passage of DNA strands through one another, resulting in a topological transformation of double-stranded DNA.
• Topoisomerase I (TOP1) relieves torsional stress by nicking one strand, while topoisomerase II (TOP2) passes a double helix through a transient double-strand break.
• This activity is essential for DNA replication, transcription, recombination, and chromosome segregation, and is a validated target of anticancer drugs such as topotecan and irinotecan.
• Dysregulated topoisomerase activity is linked to cancer, aging, and developmental defects; excessive MYC-topoisome activity triggers acute DNA damage and MYC degradation.
• CRISPR-based knockout, point mutation, knock-in, and overexpression models enable causal dissection of topoisomerase function in human cells and pathogens.
• QuickGO defines GO:0003916 as a molecular function, and its activity can be modulated by G-quadruplexes, inhibitors, and developmental cues.
Description
DNA topoisomerase activity (GO:0003916) is a fundamental molecular function that resolves the topological problems inherent to double-stranded DNA during replication, transcription, recombination, and chromosome segregation. Without this activity, the DNA helix would become overwound or entangled, leading to stalled replication forks and genome instability. The term encompasses both type I and type II topoisomerases, which catalyze transient cleavage and passage of individual DNA strands or double helices through one another, resulting in a topological transformation. Researchers study this activity to understand basic DNA metabolism and to develop therapeutics, as topoisomerase poisons are among the most widely used anticancer agents. Recent work has also revealed that topoisomerase activity is tightly regulated by DNA secondary structures such as G-quadruplexes and by oncogenic transcription factors like MYC. In this article, we provide a research-grade overview of GO:0003916, covering its definition, mechanism, key genes, disease links, and CRISPR-based methods for functional interrogation.
DNA topoisomerase activity At A Glance
| GO ID | GO:0003916 |
|---|---|
| GO term | DNA topoisomerase activity |
| Ontology | molecular_function |
| Synonym | none |
| Definition | Catalysis of the transient cleavage and passage of individual DNA strands or double helices through one another, resulting a topological transformation in double-stranded DNA. |
| Major function | Relieves torsional stress and resolves DNA entanglements during replication, transcription, recombination, and chromosome segregation. |
| Enzyme types | Type I topoisomerases (e.g., TOP1) cleave one strand; type II topoisomerases (e.g., TOP2A/TOP2B) cleave both strands. |
| Inhibitors | Camptothecin, topotecan, and irinotecan target topoisomerase I; etoposide targets topoisomerase II. |
| Regulation | Activity is modulated by G-quadruplexes, developmental stage, and oncogenic transcription factors such as MYC. |
What Is GO:0003916?
According to the Gene Ontology, GO:0003916 DNA topoisomerase activity is defined as the catalysis of the transient cleavage and passage of individual DNA strands or double helices through one another, resulting in a topological transformation in double-stranded DNA. In simpler terms, it is the enzyme activity that cuts DNA temporarily, allows strands to pass through the break, and then reseals the DNA, thereby changing its supercoiling or knotting state without altering the DNA sequence.
Why Is DNA topoisomerase activity Important in Cell Biology?
DNA topoisomerase activity is essential for maintaining genome stability and enabling fundamental DNA transactions. Its dysfunction leads to replication stress, DNA damage, and cell death, making it a central node in cancer biology and a prime target for chemotherapeutic intervention. Moreover, topoisomerase activity is required for normal development and aging, as evidenced by age-related increases in topoisomerase I activity in human chromatin and defective activity in temperature-sensitive cell mutants. Understanding GO:0003916 therefore has broad implications for basic biology, drug discovery, and disease modeling.
• Enables DNA replication and transcription by relieving positive and negative supercoiling.
• Prevents DNA entanglement and knotting during chromosome segregation.
• Target of widely used anticancer drugs such as topotecan and etoposide.
• Dysregulation causes DNA damage and is linked to oncogenic stress, as seen with MYC-topoisome activity.
• Plays a role in bacterial development, as shown by CRISPRi repression of topA in Chlamydia trachomatis.
• Activity changes with aging in human cells, suggesting a role in senescence.
• Defective topoisomerase I activity is associated with temperature-sensitive growth phenotypes in mammalian cells.
• G-quadruplexes on chromosomal DNA negatively regulate topoisomerase 1 activity, linking DNA structure to enzyme function.
• Provides a model system for studying enzyme mechanism and drug action in mycoplasmas and other organisms.
• CRISPR-based tools allow precise perturbation of topoisomerase genes for functional studies.
Mechanism, Genes and Research Methods
What Happens During DNA topoisomerase activity?
In simple terms: Topoisomerases cut DNA temporarily to let strands pass through, then seal the cut.
During DNA topoisomerase activity, the enzyme binds to double-stranded DNA and introduces a transient break. Type I topoisomerases cleave one strand, allowing the intact strand to pass through, while type II topoisomerases cleave both strands and pass a double helix through the break. This process changes the DNA's topological state, relieving supercoils and resolving knots or tangles. The reaction is ATP-dependent for type II enzymes and ATP-independent for type I enzymes. After passage, the break is resealed, restoring DNA integrity.
Catalytic cycle of type I topoisomerases
In simple terms: Type I enzymes nick one strand, rotate it, and reseal it.
Type I topoisomerases, such as human TOP1, form a covalent tyrosyl-phosphate intermediate with the 3' end of the cleaved strand. The intact strand passes through the nick, and the enzyme religates the break. This cycle relaxes both positive and negative supercoils. The activity of TOP1 can be inhibited by camptothecin and its derivatives, which stabilize the cleavage complex and convert the enzyme into a DNA-damaging agent.
Catalytic cycle of type II topoisomerases
In simple terms: Type II enzymes cut both strands and pass another DNA helix through.
Type II topoisomerases (e.g., TOP2A and TOP2B) dimerize and cleave both strands of a DNA duplex, forming covalent 5'-phosphotyrosyl linkages. ATP binding induces a conformational change that allows a second DNA helix to pass through the break, followed by religation. These enzymes are essential for decatenation of sister chromatids and for relieving supercoils ahead of replication forks. Etoposide and other topoisomerase II poisons stabilize the cleavage complex, leading to double-strand breaks and apoptosis.
Structure and Composition of DNA topoisomerase activity
In simple terms: Topoisomerases have a core domain that cuts DNA and a gate that controls strand passage.
Type I topoisomerases typically consist of a single polypeptide with a conserved core domain containing the catalytic tyrosine, a linker, and a C-terminal domain. Human TOP1 has a compact structure that wraps around the DNA. Type II enzymes are homodimers or heterodimers with an ATPase domain, a cleavage core, and a C-terminal domain. The active site includes the catalytic tyrosine and nearby residues that stabilize the transition state. These structural features enable the transient cleavage and passage of DNA strands.
Molecular Mechanism of DNA topoisomerase activity
In simple terms: The enzyme uses a tyrosine to attack DNA, forming a temporary covalent bond.
The catalytic mechanism involves nucleophilic attack by a conserved tyrosine residue on a DNA phosphodiester bond, forming a covalent enzyme-DNA intermediate and releasing a free hydroxyl group. The broken strand(s) can then rotate or pass through, and the hydroxyl group attacks the covalent bond to reseal the DNA. This mechanism is highly conserved across species. Cofactors such as Mg2+ are required for type II enzymes, while type I enzymes do not require metal ions. Regulation occurs via post-translational modifications, protein-protein interactions, and DNA secondary structures like G-quadruplexes.
Key Genes Involved in GO:0003916 DNA topoisomerase activity
The following genes encode proteins with DNA topoisomerase activity or directly regulate it, as supported by published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| TOP1 | Type I topoisomerase that relaxes supercoils by nicking one strand | Target of camptothecin and topotecan; studied in cancer and aging |
| TOP2A | Type II topoisomerase essential for replication and chromosome segregation | Target of etoposide; biomarker in cancer |
| TOP2B | Type II topoisomerase involved in transcription and development | Linked to neuronal development and drug-induced DNA damage |
| MYC | Oncogenic transcription factor that recruits topoisomerases to active promoters | Excessive MYC-topoisome activity triggers DNA damage and MYC degradation |
| TP53 | Tumor suppressor that replaces MYC in topoisome complexes after damage | p53-topoisome formation is a response to topoisomerase-induced stress |
| topA | Bacterial type I topoisomerase in Chlamydia trachomatis | CRISPRi repression reveals role in developmental cycle |
| M. fermentans topo | Topoisomerase activity in Mycoplasma fermentans | Model for studying enzyme activity in minimal genomes |
| M. pirum topo | Topoisomerase activity in Mycoplasma pirum | Comparative studies of topoisomerase function |
| DNAts mutant topo | Defective topoisomerase I in temperature-sensitive Balb/3T3 cells | Model for cell cycle and DNA replication studies |
| Aging chromatin topo | Increased topoisomerase I activity in aging human cell chromatin | Implications for senescence and aging research |
| G-quadruplex | DNA secondary structure that negatively regulates TOP1 activity | Target for modulating topoisomerase function |
| Topotecan | Small molecule inhibitor of TOP1 | Used to study TOP1 mechanism and as anticancer drug |
| Camptothecin | Natural product inhibitor of TOP1 | Tool compound for dissecting TOP1 functions |
| Etoposide | Inhibitor of TOP2 | Used in cancer therapy and as research tool |
| CRISPRi system | Targeted repression of topA in Chlamydia | Enables functional studies of essential genes |
| p53 | Tumor suppressor that interacts with topoisome | Studied in DNA damage response |
How Is DNA topoisomerase activity Regulated?
DNA topoisomerase activity is regulated at multiple levels. G-quadruplexes on chromosomal DNA negatively regulate topoisomerase 1 activity, providing a structural layer of control. Oncogenic transcription factors such as MYC recruit topoisomerases to active promoters, and excessive MYC-topoisome activity triggers acute DNA damage, MYC degradation, and replacement by a p53-topoisome. Developmental cues also regulate topoisomerase I activity, as shown in Chlamydia trachomatis where balanced activity is critical for the developmental cycle. Additionally, aging is associated with increased topoisomerase I activity in human cell chromatin.
DNA topoisomerase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| TOP1 | Cancer, drug response | KO, point mutation, overexpression in cancer cell lines |
| TOP2A | Cancer, chromosome instability | KO, knock-in of resistance mutations |
| MYC | Oncogenic stress, DNA damage | Overexpression, point mutation, KO |
| TP53 | Tumor suppression, DNA damage response | KO, knock-in of mutants |
| topA | Chlamydia developmental cycle | CRISPRi knockdown in Chlamydia |
Cancer
Dysregulated DNA topoisomerase activity is a hallmark of many cancers. TOP1 and TOP2 are overexpressed in various tumors and are targets of chemotherapeutic agents such as topotecan and etoposide. Excessive MYC-topoisome activity can cause acute DNA damage and trigger a p53-dependent response, highlighting the interplay between oncogenic transcription and topoisomerase function. Inhibitors that stabilize the enzyme-DNA cleavage complex are widely used in the clinic.
Aging and Senescence
Topoisomerase I activity increases in aging human cell chromatin, suggesting a role in age-related cellular changes. Defective topoisomerase I activity in temperature-sensitive mutants impairs DNA replication and cell cycle progression, linking topoisomerase function to cellular senescence.
Infectious Disease
Bacterial topoisomerases are essential for pathogen survival and development. In Chlamydia trachomatis, CRISPRi-mediated repression of topA reveals a critical function for balanced DNA topoisomerase I activity in the developmental cycle, suggesting potential as an antibacterial target. Topoisomerase activity has also been characterized in Mycoplasma species, which serve as models for minimal genome studies.
From DNA topoisomerase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of TOP1 affect replication fork progression? | TOP1 knockout cell line |
| How do point mutations in TOP1 alter drug sensitivity? | Point mutation knock-in via CRISPR |
| Can overexpression of MYC induce topoisomerase-mediated DNA damage? | MYC overexpression model |
| What is the role of TOP2A in chromosome segregation? | TOP2A knockout or knock-in |
| Does balanced topA activity control Chlamydia development? | CRISPRi repression of topA |
| How does aging affect topoisomerase I activity? | Aging cell chromatin models |
How to Study the DNA topoisomerase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Plasmid relaxation assay | Topoisomerase I/II activity | Enzyme kinetics and inhibitor testing |
| Decatenation assay | Topoisomerase II activity | Drug screening and mutant analysis |
| CRISPR knockout | Gene function | Loss-of-function studies |
| CRISPRi | Gene repression | Essential gene studies in bacteria |
| gamma-H2AX staining | DNA double-strand breaks | Detection of topoisomerase-induced damage |
| Comet assay | DNA strand breaks | Genotoxicity assessment |
| Cryo-EM | Protein structure | Mechanistic studies of topoisomerases |
Enzymatic assays for topoisomerase activity
Topoisomerase activity is commonly measured using plasmid relaxation or decatenation assays. These assays detect changes in DNA topology by gel electrophoresis, where relaxed or decatenated products migrate differently from supercoiled or catenated substrates. Such assays are used to screen inhibitors and to characterize mutant enzymes.
CRISPR-based genetic screens
CRISPR knockout and CRISPRi screens can identify genes that modulate sensitivity to topoisomerase poisons. For example, CRISPRi repression of topA in Chlamydia trachomatis revealed its essential role in development. Genome-wide screens can uncover synthetic lethal interactions with TOP1 or TOP2 inhibitors.
Imaging and DNA damage detection
Immunofluorescence for DNA damage markers such as gamma-H2AX and comet assays can detect topoisomerase-induced DNA breaks. Live-cell imaging of fluorescently tagged topoisomerases allows real-time visualization of enzyme dynamics at replication forks and transcription sites.
Biochemical and structural studies
Recombinant topoisomerases can be purified for biochemical assays, including cleavage complex formation and religation. Structural biology techniques such as X-ray crystallography and cryo-EM provide insights into the catalytic cycle and drug binding.
How CRISPR Can Be Used to Study GO:0003916 DNA topoisomerase activity
Knockout
CRISPR knockout of TOP1, TOP2A, or TOP2B can reveal their essential roles in cell proliferation and DNA metabolism. For example, TOP1 knockout cells are hypersensitive to camptothecin and show replication defects. Knockout of topA in Chlamydia using CRISPRi demonstrated its critical function in the developmental cycle.
Point Mutation
Point mutations in the catalytic tyrosine or drug-binding pocket of topoisomerases can be introduced via CRISPR to dissect enzyme mechanism and drug resistance. Such models help identify residues critical for cleavage and religation.
Knock-in
Knock-in of tagged topoisomerases (e.g., GFP or HA) allows live-cell imaging and proteomic analysis. Knock-in of disease-associated mutations can model human disorders linked to topoisomerase dysfunction.
Overexpression
Overexpression of TOP1 or MYC can induce topoisomerase-mediated DNA damage and activate checkpoints. These models are useful for studying oncogenic stress and the p53 response.
How EDITGENE Supports DNA topoisomerase activity Research
Researchers studying DNA topoisomerase activity-related genes often need to determine whether a candidate gene is causally involved in a specific DNA transaction or drug response. EDITGENE provides a comprehensive suite of CRISPR services to generate precisely engineered cell models, enabling rigorous functional validation of topoisomerase genes and their regulators.
Contact EDITGENE today to design your custom CRISPR model for DNA topoisomerase activity research.
Frequently Asked Questions About DNA topoisomerase activity
What is DNA topoisomerase activity?
DNA topoisomerase activity (GO:0003916) is the catalysis of transient cleavage and passage of DNA strands through one another, resulting in a topological transformation of double-stranded DNA.
What genes are involved in DNA topoisomerase activity?
Key genes include TOP1, TOP2A, TOP2B, and bacterial topA, as well as regulators like MYC and TP53.
How is DNA topoisomerase activity regulated?
It is regulated by G-quadruplexes, oncogenic transcription factors like MYC, developmental cues, and aging-related changes.
What diseases are associated with DNA topoisomerase activity?
Cancer, aging, and infectious diseases are linked to topoisomerase dysfunction.
What drugs target DNA topoisomerase activity?
Topotecan, irinotecan, and camptothecin target topoisomerase I; etoposide targets topoisomerase II.
How can I study DNA topoisomerase activity in the lab?
Common methods include plasmid relaxation assays, decatenation assays, CRISPR knockout, and DNA damage staining.
What is the difference between type I and type II topoisomerases?
Type I enzymes cleave one DNA strand, while type II enzymes cleave both strands and pass a double helix through the break.
Can CRISPR be used to study topoisomerase genes?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression are powerful tools for dissecting topoisomerase function.
What is the role of MYC in topoisomerase activity?
MYC recruits topoisomerases to active promoters; excessive MYC-topoisome activity triggers DNA damage and MYC degradation.
How does aging affect topoisomerase I activity?
Topoisomerase I activity increases in aging human cell chromatin, suggesting a role in senescence.
Conclusion
DNA topoisomerase activity (GO:0003916) is a central molecular function that safeguards genome stability and enables essential DNA transactions. Its dysregulation is implicated in cancer, aging, and infectious diseases, making it a prime target for therapeutic intervention and basic research. By leveraging CRISPR-based models and biochemical assays, researchers can dissect the precise roles of topoisomerases and their regulators, accelerating the development of novel drugs and diagnostics.
References
- 1. Liang HT et al.. 2024. G-quadruplexes on chromosomal DNA negatively regulates topoisomerase 1 activity.. Nucleic Acids Res 52(5):2142-2156 PMID: 38340342
- 2. Bali SK et al.. 2018. Activity of Topotecan toward the DNA/Topoisomerase I Complex: A Theoretical Rationalization.. Biochemistry 57(9):1542-1551 PMID: 29412654
- 3. Das SK et al.. 2024. Excessive MYC-topoisome activity triggers acute DNA damage, MYC degradation, and replacement by a p53-topoisome.. Mol Cell 84(21):4059-4078.e10 PMID: 39481385
- 4. Capranico G et al.. 2010. Dissecting the transcriptional functions of human DNA topoisomerase I by selective inhibitors: implications for physiological and therapeutic modulation of enzyme activity.. Biochim Biophys Acta 1806(2):240-50 PMID: 20600630
- 5. Shen L et al.. 2024. Targeted repression of topA by CRISPRi reveals a critical function for balanced DNA topoisomerase I activity in the Chlamydia trachomatis developmental cycle.. mBio 15(2):e0258423 PMID: 38265209
- 6. Horowitz S et al.. 1997. Characterization of DNA topoisomerase activity in two strains of Mycoplasma fermentans and in Mycoplasma pirum.. J Bacteriol 179(21):6626-32 PMID: 9352909
- 7. Zeng GC et al.. 1985. Defective DNA topoisomerase I activity in a DNAts mutant of Balb/3T3 cells.. Somat Cell Mol Genet 11(6):557-69 PMID: 3000000
- 8. Hamelin C et al.. 1984. Increased DNA topoisomerase I activity in aging human cell chromatin.. Biosci Rep 4(10):861-8 PMID: 6097322
