GO:0006301 DNA damage tolerance: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0006301 DNA damage tolerance is a biological process that allows DNA polymerases to bypass single-stranded DNA lesions during replication, preventing fork stalling and enabling completion of replication without removing the damage.
• The process is best known for its reliance on ubiquitination and sumoylation of the sliding clamp PCNA, which switches the replication machinery to error-prone or error-free bypass pathways.
• Key genes include PCNA, RAD18, RAD51, REV1, REV3L, REV7, POLH, POLI, POLK, POLN, POLQ, PRIMPOL, RAD5, and UBE2B, many of which are conserved from yeast to humans.
• DNA damage tolerance is critical for stem cell maintenance, ageing, mutagenesis, and the response to cancer therapy, making it a promising therapeutic target.
• Replicative gaps that persist after damage tolerance failure contribute to genome instability and cancer, and are now recognized as actionable vulnerabilities.
• Studying DNA damage tolerance requires integrated approaches including CRISPR knockout, point-mutation knock-in, overexpression models, and CRISPR library screening.
Description
DNA damage tolerance (GO:0006301) is a fundamental biological process that safeguards genome duplication when the DNA template is compromised. Unlike DNA repair pathways that physically remove lesions, DNA damage tolerance promotes the bypass of single-stranded DNA lesions encountered by DNA polymerases during S phase, thereby preventing replication fork stalling and allowing completion of DNA replication without removing the damage. This process is essential for cell survival under replication stress and is conserved across eukaryotes. Researchers study DNA damage tolerance because it sits at the crossroads of mutagenesis, genome instability, and cancer therapy resistance. Defects in this pathway lead to replication-associated DNA breaks, while its overactivation can drive mutagenic bypass and tumor heterogeneity. Understanding the molecular players and regulatory layers of DNA damage tolerance is therefore critical for developing targeted interventions in oncology and for interpreting genome-wide screens.
DNA damage tolerance At A Glance
| GO ID | GO:0006301 |
|---|---|
| GO term | DNA damage tolerance |
| Ontology | biological_process |
| Synonym | postreplication DNA repair; postreplication repair |
| Major function | Bypass of single-stranded DNA lesions during replication to prevent fork stalling and allow completion of DNA replication without removing the damage |
| Key regulatory event | Ubiquitination and sumoylation of PCNA |
| Conserved factors | RAD18, RAD51, REV1, REV3L, REV7, POLH, POLI, POLK, POLN, POLQ, PRIMPOL, RAD5 |
| Associated genome instability | Replicative gaps and cancer therapy resistance |
| Therapeutic relevance | Potential target in cancer therapy and stem cell biology |
What Is GO:0006301?
DNA damage tolerance is defined by the Gene Ontology as a process that promotes the bypass of single-stranded DNA lesions encountered by DNA polymerases during DNA replication, thereby preventing replication fork stalling and allowing completion of DNA replication without removing the damage. In other words, it is a damage-tolerance mechanism that helps the replisome move past obstacles, rather than repairing them, ensuring that replication finishes even when the template is imperfect.
Why Is DNA damage tolerance Important in Cell Biology?
DNA damage tolerance is important because it determines whether cells survive replication stress at the cost of potential mutagenesis. This process allows replication to complete despite unrepaired lesions, but it can also introduce mutations through error-prone polymerases, linking it directly to cancer initiation and evolution. In stem cells, proper regulation of DNA damage tolerance is critical for maintaining genomic integrity and preventing premature ageing. Moreover, many chemotherapeutic agents create DNA lesions that require damage tolerance for cancer cell survival, making this pathway a promising target for sensitizing tumors to therapy.
• Prevents replication fork stalling and allows completion of DNA replication despite persistent lesions.
• Central to mutagenesis and genome instability through error-prone bypass polymerases.
• Regulated by PCNA ubiquitination and sumoylation, which determine pathway choice.
• Critical for stem cell maintenance and tissue homeostasis during ageing.
• Contributes to cancer therapy resistance by enabling survival under genotoxic stress.
• Replicative gaps arising from defective damage tolerance are linked to cancer and genome instability.
• Conserved from yeast to humans, with RAD5 and Rad5-like factors playing key roles.
• PrimPol-mediated re-priming provides an alternative damage tolerance mechanism in human cells.
• Replisome-dependent control of damage tolerance is emerging as a regulatory paradigm.
• Potential therapeutic target for cancer and age-related diseases.
What Happens During DNA damage tolerance?
Lesion recognition and PCNA modification
In simple terms: When the DNA copying machine hits damage, a clamp on the DNA gets tagged with a small protein to call for help.
During DNA replication, single-stranded DNA lesions block the progression of replicative polymerases. The sliding clamp PCNA is monoubiquitinated at lysine 164 by the RAD6-RAD18 complex, a key event that initiates DNA damage tolerance. This modification serves as a platform for recruiting specialized translesion synthesis (TLS) polymerases or for further polyubiquitination that promotes error-free bypass. Sumoylation of PCNA at the same residue can also occur and may influence pathway choice.
Translesion synthesis (TLS) pathway
In simple terms: Specialized copy machines that can read past damage are recruited to finish the job, though they sometimes make mistakes.
Monoubiquitinated PCNA recruits Y-family polymerases such as POLH, POLI, POLK, and REV1, which can insert nucleotides opposite the lesion. REV1 acts as a scaffold and inserts a cytosine opposite certain lesions, while REV3L (the catalytic subunit of polymerase zeta) together with REV7 extends the primer after the lesion. This TLS pathway is error-prone and contributes to mutagenesis, but it is essential for survival under severe replication stress.
Error-free damage avoidance
In simple terms: Instead of copying past the damage directly, the cell can use the newly made sister strand as a template to bypass the problem accurately.
Polyubiquitination of PCNA by the RAD5/HLTF/SHPRH ubiquitin ligases promotes error-free damage avoidance, often involving template switching. In this pathway, the stalled nascent strand uses the newly synthesized sister chromatid as a template, avoiding the lesion and maintaining high fidelity. This mechanism is conserved and requires RAD51 and other homologous recombination factors.
Re-priming and replicative gaps
In simple terms: Sometimes the copying machine restarts downstream of the damage, leaving a gap that must be filled later.
PrimPol, a primase-polymerase, can re-prime DNA synthesis downstream of lesions, leaving single-stranded gaps behind the replication fork. These replicative gaps are subsequently filled by damage tolerance pathways, and failure to do so leads to genome instability and cancer. The interplay between re-priming and gap filling is a major area of current research.
Resolution and fork restart
In simple terms: After bypass, the replication machinery must be properly reset to continue and complete genome duplication.
Following bypass, the replication fork must be restarted and the remaining gaps filled. This involves the coordinated action of TLS, template switching, and possibly homologous recombination. The Rad5 protein, a conserved ubiquitin ligase, plays a key role in this resolution, and its function is also linked to telomere replication. Defects in resolution lead to persistent gaps, fork collapse, and DNA breaks.
Key Genes Involved in GO:0006301 DNA damage tolerance
The following genes and proteins are central to DNA damage tolerance, as supported by the cited literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| PCNA | Sliding clamp; ubiquitination and sumoylation target | Central regulator of pathway choice |
| RAD18 | E3 ubiquitin ligase; monoubiquitinates PCNA | Initiates damage tolerance |
| RAD51 | Homologous recombination factor; template switching | Error-free damage avoidance |
| REV1 | Y-family polymerase; scaffold for TLS | Translesion synthesis |
| REV3L | Catalytic subunit of polymerase zeta | TLS extension |
| REV7 | Accessory subunit of polymerase zeta | TLS regulation |
| POLH | Y-family polymerase; bypasses UV lesions | Xeroderma pigmentosum variant |
| POLI | Y-family polymerase; bypasses various lesions | TLS |
| POLK | Y-family polymerase; bypasses bulky lesions | TLS |
| POLN | A-family polymerase; bypasses lesions | TLS |
| POLQ | A-family polymerase; microhomology-mediated end joining | Backup damage tolerance |
| PRIMPOL | Primase-polymerase; re-priming | Replicative gap formation |
| RAD5 | Ubiquitin ligase; polyubiquitinates PCNA | Error-free damage avoidance |
| UBE2B | E2 ubiquitin-conjugating enzyme | PCNA ubiquitination |
| HLTF | Ubiquitin ligase; polyubiquitinates PCNA | Error-free damage avoidance |
| SHPRH | Ubiquitin ligase; polyubiquitinates PCNA | Error-free damage avoidance |
| MAD2L2 | REV7 paralog; involved in TLS and other processes | TLS regulation |
How Is DNA damage tolerance Regulated?
DNA damage tolerance is tightly regulated at multiple levels. The key regulatory event is the ubiquitination and sumoylation of PCNA, which determines whether cells use error-prone TLS or error-free template switching. This modification is controlled by the RAD6-RAD18 complex and reversed by deubiquitinating enzymes such as USP1. Replisome-dependent control of damage tolerance ensures that bypass occurs only when the fork is stalled and in a timely manner. Additionally, the abundance and localization of TLS polymerases are regulated transcriptionally and post-translationally, and PrimPol activity is modulated to balance re-priming and gap formation. In stem cells, damage tolerance is also influenced by developmental and ageing-related signals.
DNA damage tolerance and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| POLH | Xeroderma pigmentosum variant; skin cancer | Knockout or point-mutation knock-in in keratinocytes |
| REV3L | Cancer therapy resistance; genome instability | Knockout in cancer cell lines; overexpression models |
| PCNA | Cancer; potential target for sensitization | Point-mutation knock-in of K164R; ubiquitination-deficient models |
| RAD51 | Cancer predisposition; homologous recombination defects | Knockout or conditional knockout in stem cells |
| PRIMPOL | Replication stress; cancer | Knockout and overexpression in cancer cell lines |
Cancer and therapy resistance
DNA damage tolerance is a double-edged sword in cancer. It allows cancer cells to survive chemotherapy and radiotherapy by bypassing DNA lesions, contributing to therapy resistance. Overexpression of TLS polymerases such as POLH, POLI, and REV3L is associated with poor prognosis in various cancers. Targeting damage tolerance pathways, for example by inhibiting PCNA ubiquitination or specific TLS polymerases, is a promising strategy to sensitize tumors to DNA-damaging agents.
Genome instability and cancer predisposition
Defects in error-free damage tolerance lead to the accumulation of replicative gaps and genome instability, which can predispose to cancer. Mutations in genes such as POLH cause xeroderma pigmentosum variant, characterized by extreme UV sensitivity and skin cancer predisposition due to defective translesion synthesis. Similarly, loss of RAD5/HLTF/SHPRH function is linked to genomic instability and cancer.
Ageing and stem cell function
DNA damage tolerance is essential for stem cell maintenance, and its decline contributes to ageing and age-related diseases. In stem cells, error-free damage tolerance is favored to preserve genomic integrity, but with age, the balance may shift toward error-prone pathways, leading to mutation accumulation. Understanding this regulation may provide insights into ageing and regenerative medicine.
From DNA damage tolerance-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of a candidate gene impair damage tolerance? | CRISPR knockout cell lines (e.g., HEK293T, U2OS) |
| Does a specific PCNA modification (e.g., K164) drive pathway choice? | Point-mutation knock-in of PCNA K164R |
| Can a tagged version of a TLS polymerase be tracked in live cells? | Knock-in of fluorescent or epitope tags (e.g., GFP, HA) |
| Does overexpression of a TLS polymerase increase mutagenesis? | Doxycycline-inducible overexpression cell lines |
| Which genes are essential for survival under replication stress? | Genome-wide CRISPR library screening |
| What are the global consequences of damage tolerance defects? | RNA-seq, proteomics, and phosphoproteomics in KO models |
How to Study the DNA damage tolerance Process
| Method | What It Measures | Typical Application |
|---|---|---|
| CRISPR knockout | Gene function loss | Assess survival and mutagenesis after DNA damage |
| Point-mutation knock-in | Specific amino acid function | Study PCNA ubiquitination site mutants |
| CRISPR library screening | Genome-wide fitness under stress | Identify synthetic lethal targets |
| RNA-seq | Transcriptional changes | Measure TLS polymerase expression |
| Proteomics | Protein abundance and modifications | Quantify PCNA ubiquitination |
| Live-cell imaging | Subcellular localization and dynamics | Track damage tolerance foci |
| Single-molecule analysis | Bypass efficiency and gap formation | Measure lesion bypass in vitro |
CRISPR knockout and point-mutation models
CRISPR-Cas9 knockout is widely used to delete genes involved in DNA damage tolerance, such as REV1, REV3L, and POLH, to assess their role in survival and mutagenesis. Point-mutation knock-in, for example of PCNA K164R, allows precise interrogation of ubiquitination-dependent pathways. These models are complemented by overexpression systems to study gain-of-function effects.
Genome-wide CRISPR library screening
CRISPR library screening enables unbiased identification of genes that modulate sensitivity to DNA-damaging agents. Screens have revealed novel damage tolerance factors and synthetic lethal interactions. Such screens are powerful for discovering therapeutic targets in cancers with defects in specific DNA repair pathways.
Transcriptomics and proteomics
RNA-seq and proteomics can quantify changes in gene expression and protein abundance upon damage tolerance perturbation. For example, loss of RAD18 alters the expression of TLS polymerases and other stress-response genes. Phosphoproteomics can reveal signaling changes downstream of replication stress.
Imaging and single-molecule analysis
Live-cell imaging of fluorescently tagged PCNA, REV1, or PRIMPOL allows real-time visualization of damage tolerance foci and replication fork dynamics. Single-molecule approaches can measure bypass efficiency and gap formation. These methods provide spatial and temporal resolution of damage tolerance processes.
How CRISPR Can Be Used to Study GO:0006301 DNA damage tolerance
Knockout
CRISPR knockout of DNA damage tolerance genes such as REV1, REV3L, POLH, and RAD18 is used to determine their contribution to cell survival, mutagenesis, and therapy resistance. Knockout models are also valuable for validating hits from CRISPR screens.
Point Mutation
Point-mutation knock-in allows precise editing of key residues, such as PCNA K164, to dissect ubiquitination-dependent functions. This approach is essential for understanding how post-translational modifications regulate pathway choice.
Knock-in
Knock-in of tags (e.g., GFP, HA, or BirA) into endogenous loci enables visualization and purification of damage tolerance proteins under native regulation. This is particularly useful for studying dynamic recruitment to stalled forks.
Overexpression
Overexpression of TLS polymerases or PCNA mutants can model the elevated damage tolerance seen in cancer cells and test whether it drives mutagenesis or therapy resistance. Inducible systems allow controlled expression to avoid toxicity.
How EDITGENE Supports DNA damage tolerance Research
Researchers studying DNA damage tolerance-related genes often need to determine whether a candidate gene is causally involved in lesion bypass, mutagenesis, or therapy response. EDITGENE provides a comprehensive suite of CRISPR services to create precisely engineered cell models for such studies.
Contact EDITGENE today to design your custom CRISPR model for DNA damage tolerance research.
Frequently Asked Questions About DNA damage tolerance
What is DNA damage tolerance (GO:0006301)?
DNA damage tolerance is a biological process that allows DNA polymerases to bypass single-stranded DNA lesions during replication, preventing fork stalling and enabling completion of replication without removing the damage.
What genes are involved in DNA damage tolerance?
Key genes include PCNA, RAD18, RAD51, REV1, REV3L, REV7, POLH, POLI, POLK, POLN, POLQ, PRIMPOL, RAD5, UBE2B, HLTF, and SHPRH.
How is DNA damage tolerance regulated?
It is primarily regulated by ubiquitination and sumoylation of PCNA, which determine whether error-prone or error-free bypass is used.
What is the difference between DNA repair and DNA damage tolerance?
DNA repair removes lesions, while DNA damage tolerance bypasses them without removal, allowing replication to finish at the cost of potential mutations.
Why is DNA damage tolerance important in cancer?
It enables cancer cells to survive DNA-damaging therapies and contributes to mutagenesis and therapy resistance, making it a therapeutic target.
What are translesion synthesis polymerases?
They are specialized enzymes such as POLH, POLI, POLK, and REV1 that can copy past DNA lesions, albeit with lower fidelity.
What is the role of PCNA ubiquitination in damage tolerance?
Monoubiquitination of PCNA at K164 recruits TLS polymerases, while polyubiquitination promotes error-free template switching.
How can CRISPR be used to study DNA damage tolerance?
CRISPR knockout, point-mutation knock-in, and overexpression models allow functional dissection of damage tolerance genes and their roles in therapy response.
What diseases are linked to defective DNA damage tolerance?
Defects are linked to xeroderma pigmentosum variant, cancer predisposition, and genome instability; overactivation contributes to therapy resistance.
What methods are used to study DNA damage tolerance?
Common methods include CRISPR screens, RNA-seq, proteomics, live-cell imaging, and single-molecule assays.
Conclusion
DNA damage tolerance (GO:0006301) is a vital process that ensures replication completion under stress, but its dysregulation drives mutagenesis and cancer. The field has advanced significantly in understanding the molecular players, especially PCNA ubiquitination and TLS polymerases, yet many questions remain about pathway choice and therapeutic targeting. Continued research using CRISPR models and genome-wide screens will uncover new vulnerabilities and opportunities for intervention.
References
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- 2. Fan L et al.. 2020. DNA-damage tolerance through PCNA ubiquitination and sumoylation.. Biochem J 477(14):2655-2677 PMID: 32726436
- 3. Ler AAL et al.. 2021. DNA Damage Tolerance Pathways in Human Cells: A Potential Therapeutic Target.. Front Oncol 11:822500 PMID: 35198436
- 4. Pilzecker B et al.. 2019. DNA damage tolerance in stem cells, ageing, mutagenesis, disease and cancer therapy.. Nucleic Acids Res 47(14):7163-7181 PMID: 31251805
- 5. Falbo L et al.. 2026. Replicative gaps in DNA damage tolerance, genome instability, and cancer therapy.. Mol Cell 86(7):1200-1216 PMID: 41864203
- 6. Mattarocci S. 2025. The DNA damage tolerance factor Rad5 and telomere replication.. Curr Genet 71(1):11 PMID: 40418329
- 7. Boldinova EO et al.. 2023. Regulation of Human DNA Primase-Polymerase PrimPol.. Biochemistry (Mosc) 88(8):1139-1155 PMID: 37758313
- 8. Zhang T et al.. 2022. The inner workings of replisome-dependent control of DNA damage tolerance.. Genes Dev 36(3-4):103-105 PMID: 35193944
