GO:0017065 single-strand selective uracil DNA N-glycosylase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0017065 describes the catalytic activity of enzymes that remove uracil from single-stranded DNA by cleaving the N-C1' glycosidic bond, leaving an apyrimidinic (AP) site.
• This activity is a critical first step in the base excision repair (BER) pathway that protects genome integrity against uracil misincorporation and cytosine deamination.
• The enzyme responsible in humans is uracil DNA glycosylase (UNG), which exists in nuclear and mitochondrial isoforms generated by alternative splicing.
• Species differences exist between human and mouse UNG, particularly in the context of adaptive immunity and class switch recombination.
• Defects in uracil excision are linked to immunodeficiency, cancer predisposition, and altered drug responses.
• CRISPR-based models (knockout, point mutation, knock-in, overexpression) enable precise dissection of GO:0017065 in disease and immunity.
Description
GO:0017065, single-strand selective uracil DNA N-glycosylase activity, is a molecular function that initiates the removal of uracil from DNA. Uracil can arise in DNA either by misincorporation of dUTP during replication or by spontaneous deamination of cytosine, both of which are mutagenic if left unrepaired. The enzyme catalyzing this reaction recognizes uracil in single-stranded DNA contexts and cleaves the N-C1' glycosidic bond, releasing the free base and creating an apyrimidinic (AP) site that is further processed by the base excision repair (BER) machinery. This activity is essential for maintaining genomic stability and has been studied extensively in the context of adaptive immunity, where it contributes to somatic hypermutation and class switch recombination. Researchers investigating DNA repair, mutagenesis, and immune diversification rely on precise characterization of this activity to understand disease mechanisms and to develop therapeutic strategies.
single-strand selective uracil DNA N-glycosylase activity At A Glance
| GO ID | GO:0017065 |
|---|---|
| GO term | single-strand selective uracil DNA N-glycosylase activity |
| Ontology | molecular_function |
| Synonym | single-strand selective monofunctional uracil-DNA glycosylase activity |
| Major function | Removal of uracil from single-stranded DNA via cleavage of the N-C1' glycosidic bond, generating an AP site |
| EC number | 3.2.2.- |
| Substrates | Uracil in single-stranded DNA |
| Products | Free uracil and an apyrimidinic (AP) site in DNA |
| Pathway context | Base excision repair (BER) |
What Is GO:0017065?
Single-strand selective uracil DNA N-glycosylase activity (GO:0017065) is defined as the catalysis of the cleavage of the N-C1' glycosidic bond between a damaged DNA base (uracil) and the deoxyribose sugar, releasing a free base and leaving an apyrimidinic (AP) site. Enzymes with this activity recognize and remove uracil bases present specifically in single-stranded DNA, distinguishing them from other uracil glycosylases that act on double-stranded DNA.
Why Is single-strand selective uracil DNA N-glycosylase activity Important in Cell Biology?
GO:0017065 is essential for genome maintenance because uracil in DNA is a common premutagenic lesion. If unrepaired, uracil can pair with adenine during replication, leading to C:G to T:A transition mutations. The single-strand selective uracil DNA N-glycosylase activity initiates the repair of such lesions, thereby preventing mutations that can drive cancer and other genetic diseases. Moreover, this activity is co-opted by the immune system to generate antibody diversity through somatic hypermutation and class switch recombination, highlighting its dual role in protection and physiological diversification.
• Prevents C:G to T:A transition mutations caused by cytosine deamination or dUTP misincorporation.
• Initiates base excision repair (BER) at uracil lesions in single-stranded DNA contexts.
• Plays a central role in adaptive immunity by contributing to somatic hypermutation and class switch recombination.
• Deficiency leads to immunodeficiency with hyper-IgM syndrome in humans.
• Altered expression is associated with cancer progression and resistance to certain chemotherapies.
• Species-specific differences between human and mouse UNG affect immune diversification mechanisms.
• Target for understanding mutagenesis and for developing anti-cancer strategies.
• Important for mitochondrial DNA maintenance due to mitochondrial UNG isoforms.
• Enables precise genome editing research by providing a model for base excision repair studies.
• Serves as a paradigm for structure-function studies of monofunctional glycosylases.
What Happens During single-strand selective uracil DNA N-glycosylase activity?
Recognition of uracil in single-stranded DNA
In simple terms: The enzyme scans DNA and finds uracil, a base that should not be there.
The enzyme binds to DNA and specifically recognizes uracil bases that are present in single-stranded regions. This selectivity is achieved through a DNA-binding pocket that accommodates uracil while excluding normal bases such as thymine or cytosine. The recognition step is crucial for avoiding excision of legitimate bases and for targeting the enzyme to sites of damage.
Cleavage of the N-C1' glycosidic bond
In simple terms: The enzyme cuts the bond that holds uracil to the DNA backbone.
Once uracil is bound, the enzyme catalyzes the hydrolysis of the N-C1' glycosidic bond between the uracil base and the deoxyribose sugar. This cleavage releases free uracil and creates an apyrimidinic (AP) site in the DNA. The reaction is monofunctional, meaning it does not possess an intrinsic AP-lyase activity; the AP site is subsequently processed by other BER enzymes.
Generation of an AP site and handoff to BER
In simple terms: After uracil is removed, a gap is left that other repair proteins fix.
The AP site generated by the glycosylase is a substrate for AP endonuclease (APE1), which incises the DNA backbone. This incision creates a single-strand break that is further processed by DNA polymerase beta and DNA ligase III/XRCC1, completing the base excision repair pathway. The coordination between the glycosylase and downstream BER factors ensures efficient repair and prevents accumulation of toxic intermediates.
Role in somatic hypermutation and class switch recombination
In simple terms: The enzyme also helps the immune system make better antibodies.
In activated B cells, the single-strand selective uracil DNA N-glycosylase activity is recruited to immunoglobulin loci where it removes uracils generated by activation-induced cytidine deaminase (AID). The resulting AP sites are processed by error-prone polymerases to introduce mutations (somatic hypermutation) or to create double-strand breaks that facilitate class switch recombination. This process is essential for generating high-affinity antibodies of different isotypes.
Key Genes Involved in GO:0017065 single-strand selective uracil DNA N-glycosylase activity
The following genes and proteins are directly involved in or regulate single-strand selective uracil DNA N-glycosylase activity (GO:0017065).
| Gene | Major Role | Research Relevance |
|---|---|---|
| UNG | Encodes the uracil DNA glycosylase enzyme responsible for GO:0017065 | Central to BER and adaptive immunity; mutations cause immunodeficiency |
| AICDA | Activation-induced cytidine deaminase, generates uracil in immunoglobulin loci | Initiates somatic hypermutation and class switch recombination |
| APE1 | AP endonuclease, processes AP sites generated by UNG | Key downstream BER factor; target for cancer therapy |
| XRCC1 | Scaffold protein in BER, interacts with ligase III | Required for efficient repair of AP sites |
| LIG3 | DNA ligase III, seals nicks after BER | Essential for BER completion |
| POLB | DNA polymerase beta, fills gaps during BER | Important for single-nucleotide BER |
| PCNA | Proliferating cell nuclear antigen, coordinates BER | Regulates UNG recruitment to replication foci |
| RPA | Single-stranded DNA-binding protein, facilitates UNG activity | Enhances uracil excision on ssDNA |
| SMUG1 | Single-strand selective monofunctional uracil DNA glycosylase | Backup glycosylase with overlapping specificity |
| TDG | Thymine DNA glycosylase, acts on mismatched bases | Distinct from UNG but shares BER pathway |
| MBD4 | Methyl-CpG-binding domain protein 4, glycosylase | Repairs deaminated methylcytosine |
| DUT | Deoxyuridine triphosphatase, prevents dUTP incorporation | Reduces uracil load in DNA |
| POLD1 | DNA polymerase delta subunit, involved in replication | May influence uracil incorporation |
| POLE | DNA polymerase epsilon, replication proofreading | Mutations linked to hypermutation |
| ATM | Ataxia telangiectasia mutated, DNA damage response kinase | Coordinates repair with cell cycle checkpoints |
| TP53 | Tumor suppressor, responds to DNA damage | Mutated in many cancers with repair defects |
| BRCA1 | Homologous recombination repair | Interacts with BER pathways |
| BRCA2 | Homologous recombination repair | Synthetic lethality with BER defects |
How Is single-strand selective uracil DNA N-glycosylase activity Regulated?
The activity of single-strand selective uracil DNA N-glycosylase is regulated at multiple levels. UNG expression is cell-cycle dependent, peaking during S phase to handle uracil incorporated during replication. Post-translational modifications, including phosphorylation and ubiquitination, modulate UNG stability and localization. Interaction with PCNA and RPA enhances its recruitment to replication forks and single-stranded DNA regions. Additionally, AID expression is tightly controlled in B cells, indirectly regulating the demand for UNG activity during immune diversification.
single-strand selective uracil DNA N-glycosylase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| UNG | Immunodeficiency with hyper-IgM syndrome | Ung knockout mouse; patient-derived iPSCs |
| AICDA | Hyper-IgM syndrome type 2 | Aicda knockout mouse; B cell culture |
| TP53 | Li-Fraumeni syndrome, cancer | Tp53 knockout; xenograft models |
| BRCA1/2 | Hereditary breast and ovarian cancer | Conditional knockout; organoids |
| POLB | Cancer susceptibility, chemosensitivity | Polb knockout; CRISPR knock-in of variants |
Immunodeficiency with hyper-IgM syndrome
Biallelic mutations in UNG cause a rare form of immunodeficiency characterized by elevated IgM and impaired class switch recombination. Patients suffer from recurrent infections due to defective antibody diversification. This condition directly links GO:0017065 to human immune function.
Cancer predisposition and mutagenesis
Deficiency in uracil excision leads to increased mutation rates and genomic instability, predisposing to various cancers. UNG expression is altered in several tumor types, and loss of function can confer resistance to certain chemotherapeutic agents that rely on uracil misincorporation, such as 5-fluorouracil and antifolates.
Neurological and mitochondrial disorders
Mitochondrial UNG isoforms are critical for maintaining mitochondrial DNA integrity. Defects in uracil repair in mitochondria have been associated with neurodegenerative diseases and aging. However, direct evidence linking GO:0017065 to specific neurological disorders is still emerging.
From single-strand selective uracil DNA N-glycosylase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does UNG loss impair class switch recombination? | UNG knockout mouse or B cell line |
| What is the impact of a catalytic point mutation in UNG? | Point mutation knock-in via CRISPR |
| How does UNG interact with PCNA at replication forks? | Tagged knock-in (e.g., GFP-UNG) |
| Can UNG overexpression protect against mutagenesis? | Overexpression cell lines |
| What are the off-target effects of UNG deficiency? | CRISPR library screening |
| Does mitochondrial UNG have distinct functions? | Isoform-specific knockout |
How to Study the single-strand selective uracil DNA N-glycosylase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Uracil glycosylase assay | Enzymatic removal of uracil from DNA | Quantify GO:0017065 in vitro |
| CRISPR knockout screen | Gene essentiality and synthetic lethality | Identify modifiers of uracil repair |
| Whole-genome sequencing | Mutation burden and signatures | Assess genomic instability |
| RNA-seq | Transcriptional changes upon UNG loss | Uncover compensatory pathways |
| ChIP-seq | Genome-wide binding of UNG | Map uracil repair sites |
| Proteomics (AP-MS) | Protein-protein interactions | Discover UNG complexes |
| Comet assay | DNA single-strand breaks | Measure repair intermediates |
| Immunofluorescence | Subcellular localization of UNG | Study mitochondrial vs nuclear isoforms |
Enzymatic activity assays
Uracil DNA glycosylase activity can be measured using oligonucleotide substrates containing uracil, followed by cleavage with AP endonuclease and gel electrophoresis. This method directly quantifies GO:0017065 in cell lysates or purified protein fractions.
CRISPR-based genetic screens
Genome-wide CRISPR knockout or activation screens can identify genes that modulate sensitivity to uracil-inducing agents. Such screens help uncover synthetic lethal interactions and pathways that compensate for loss of GO:0017065.
Next-generation sequencing for mutation signatures
Whole-genome or exome sequencing can detect C:G to T:A transition mutations, a hallmark of uracil misrepair. Comparing mutation spectra in UNG-proficient versus deficient cells reveals the contribution of GO:0017065 to genome stability.
Proteomics and interactomics
Affinity purification coupled with mass spectrometry can identify proteins that interact with UNG, revealing regulatory complexes and post-translational modifications that control its activity.
How CRISPR Can Be Used to Study GO:0017065 single-strand selective uracil DNA N-glycosylase activity
Knockout
CRISPR knockout of UNG or other genes in the pathway (e.g., APE1, XRCC1) creates cell models to study the consequences of losing GO:0017065. These models are valuable for assessing sensitivity to DNA-damaging agents and for identifying synthetic lethal interactions.
Point Mutation
Introducing specific point mutations in the catalytic domain of UNG (e.g., aspartate to asparagine) via CRISPR base editing or HDR allows dissection of the enzymatic mechanism and separation of catalytic activity from protein-protein interactions.
Knock-in
Knock-in of epitope tags (e.g., FLAG, GFP) or fluorescent reporters at the endogenous UNG locus enables real-time imaging and proteomic analysis of the enzyme under physiological conditions.
Overexpression
CRISPR activation (CRISPRa) or lentiviral overexpression of UNG can be used to study the effects of elevated glycosylase activity on mutation rates, drug resistance, and immune diversification.
How EDITGENE Supports single-strand selective uracil DNA N-glycosylase activity Research
Researchers studying single-strand selective uracil DNA N-glycosylase activity-related genes often need to determine whether a candidate gene is causally involved in DNA repair, mutagenesis, or immune diversification. 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 single-strand selective uracil DNA N-glycosylase activity research.
Frequently Asked Questions About single-strand selective uracil DNA N-glycosylase activity
What is single-strand selective uracil DNA N-glycosylase activity?
It is a molecular function (GO:0017065) that removes uracil from single-stranded DNA by cleaving the N-C1' glycosidic bond, leaving an AP site.
What genes are involved in single-strand selective uracil DNA N-glycosylase activity?
The primary gene is UNG, which encodes uracil DNA glycosylase. Other related genes include AICDA, APE1, XRCC1, and SMUG1.
What is the role of UNG in the immune system?
UNG is essential for somatic hypermutation and class switch recombination, processes that generate antibody diversity.
How is single-strand selective uracil DNA N-glycosylase activity measured?
It is typically measured using oligonucleotide substrates containing uracil, followed by cleavage with AP endonuclease and gel electrophoresis.
What diseases are associated with defects in uracil DNA glycosylase?
Defects cause immunodeficiency with hyper-IgM syndrome and are linked to cancer predisposition.
What is the difference between UNG and SMUG1?
Both are uracil DNA glycosylases, but UNG is the major enzyme for single-strand selective activity, while SMUG1 acts as a backup with broader specificity.
Can CRISPR be used to study single-strand selective uracil DNA N-glycosylase activity?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models enable precise functional studies.
What are the substrates of GO:0017065?
The substrate is uracil in single-stranded DNA; the products are free uracil and an apyrimidinic (AP) site.
How does UNG contribute to cancer?
Loss of UNG increases mutation rates and genomic instability, which can drive cancer development and affect drug responses.
What model systems are used to study GO:0017065?
Common models include UNG knockout mice, patient-derived cells, and CRISPR-engineered cell lines.
Conclusion
GO:0017065, single-strand selective uracil DNA N-glycosylase activity, is a fundamental DNA repair function that safeguards genome integrity and supports adaptive immunity. Its central enzyme, UNG, removes uracil from single-stranded DNA, initiating base excision repair. Dysregulation of this activity leads to immunodeficiency and cancer, making it a critical target for research and therapeutic development. CRISPR-based models offer powerful tools to dissect its mechanism and role in disease.
References
- 1. Doseth B et al.. 2011. Uracil-DNA glycosylase in base excision repair and adaptive immunity: species differences between man and mouse.. J Biol Chem 286(19):16669-80 PMID: 21454529
