UNG Protein
<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">UNG Protein (Uracil-DNA Glycosylase)</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td><strong>UNG</strong></td>
</tr>
<tr>
<td class="label">Protein Name</td>
<td>Uracil-DNA Glycosylase</td>
</tr>
<tr>
<td class="label">Alternative Names</td>
<td>UNG, UNG1, UNG2, UDG</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td><a href="https://www.uniprot.org/uniprot/P13051" target="_blank">P13051</a></td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/7341" target="_blank">7341</a></td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>12q24.31</td>
</tr>
<tr>
<td class="label">Protein Length</td>
<td>313 amino acids</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~36 kDa</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>UNG family, uracil-DNA glycosylase superfamily</td>
</tr>
<tr>
<td class="label">Primary Localization</td>
<td>Nucleus, mitochondria</td>
</tr>
<tr>
<td class="label">Brain Expression</td>
<td>Hippocampus, cortex, substantia nigra, cerebellum</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/dementia" style="color:#ef9a9a">Dementia</a>, <a href="/wiki/depression" style="color:#ef9a9a">Depression</a>, <a href="/wiki/neurodegeneration" style="color:#ef9a9a">Neurodege
...UNG Protein
<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">UNG Protein (Uracil-DNA Glycosylase)</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td><strong>UNG</strong></td>
</tr>
<tr>
<td class="label">Protein Name</td>
<td>Uracil-DNA Glycosylase</td>
</tr>
<tr>
<td class="label">Alternative Names</td>
<td>UNG, UNG1, UNG2, UDG</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td><a href="https://www.uniprot.org/uniprot/P13051" target="_blank">P13051</a></td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/7341" target="_blank">7341</a></td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>12q24.31</td>
</tr>
<tr>
<td class="label">Protein Length</td>
<td>313 amino acids</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~36 kDa</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>UNG family, uracil-DNA glycosylase superfamily</td>
</tr>
<tr>
<td class="label">Primary Localization</td>
<td>Nucleus, mitochondria</td>
</tr>
<tr>
<td class="label">Brain Expression</td>
<td>Hippocampus, cortex, substantia nigra, cerebellum</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/dementia" style="color:#ef9a9a">Dementia</a>, <a href="/wiki/depression" style="color:#ef9a9a">Depression</a>, <a href="/wiki/neurodegeneration" style="color:#ef9a9a">Neurodegeneration</a>, <a href="/wiki/stroke" style="color:#ef9a9a">Stroke</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">20 edges</a></td>
</tr>
</table>
UNG Protein (Uracil-DNA Glycosylase)
Overview
UNG (Uracil-DNA Glycosylase) is a critical DNA repair enzyme that maintains genomic integrity by removing uracil from DNA. As the primary enzyme in the base excision repair (BER) pathway, UNG recognizes and excises uracil that arises from either cytosine deamination (producing deoxyuridine) or misincorporation of dUTP during DNA replication. This activity prevents the accumulation of C→T transition mutations, which are among the most common mutations in human cancers and age-related diseases.
In neurons, UNG plays a particularly important role due to the post-mitotic nature of these cells—the inability to dilute DNA damage through cell division means that unrepaired lesions accumulate over time. Decreased UNG activity has been documented in Alzheimer's disease, Parkinson's disease, Huntington's disease, and normal aging, contributing to the progressive accumulation of mutations in neuronal genomes.
The gene is located on chromosome 12q24.31 and encodes a 313-amino acid protein with both nuclear and mitochondrial isoforms.
Gene and Protein Structure
Genomic Organization
The UNG gene (NCBI Gene ID: 7341) spans approximately 6.5 kb on chromosome 12q24.31 and consists of 7 exons. The gene utilizes alternative transcription start sites and splicing to produce multiple protein isoforms with distinct subcellular localizations.
Protein Architecture
Mermaid diagram (expand to render)
UNG2 (Nuclear): Full-length isoform (313 aa) with N-terminal nuclear localization signal
UNG1 (Mitochondrial): N-terminally truncated isoform targeting mitochondria
UNG3: Testis-specific isoform
UNG5: Cytoplasmic variantCrystal Structure
The crystal structure of human UNG (PDB: 1AKZ, 1EMH, 2D7H) reveals a compact α/β fold with:
- A catalytic core containing the active site motif (Asn204-His210)
- A β-strand "leucine-binding pocket" for DNA intercalation
- Flexible loops that contact the DNA substrate
- A conserved histidine (His268) critical for catalysis
Normal Function in the Nervous System
Base Excision Repair Pathway
UNG initiates the base excision repair pathway:
Mermaid diagram (expand to render)
Enzymatic Mechanism
UNG catalyzes the removal of uracil through a base-flipping mechanism:
DNA binding: UNG intercalates into the DNA helix, flipping the uracil base out of the stack
Catalysis: The active site residues (Asn204, His268, Asp273) hydrolyze the N-glycosidic bond
Product release: The AP site is generated and handed off to AP endonuclease (APE1)Neuronal Functions
In neurons, UNG maintains:
Nuclear genome integrity: Prevents accumulation of C→T transitions in nuclear DNA
Mitochondrial DNA repair: Protects mtDNA from the high mutation rate from reactive oxygen species
Transcriptional fidelity: Ensures accurate transcription by maintaining DNA template integrity
Synaptic plasticity: Supports the DNA remodeling required for long-term potentiation
Role in Neurodegenerative Diseases
Alzheimer's Disease
DNA Repair Deficits
In AD, UNG activity is significantly reduced:
Enzyme level reduction: UNG protein and mRNA levels are decreased in hippocampus and cortex
Activity impairment: Catalytic efficiency of residual UNG is reduced by oxidative modification
Isoform-specific loss: Nuclear UNG2 shows greater decline than mitochondrial UNG1Pathogenic Consequences
Reduced UNG in AD leads to:
Mutation accumulation: C→T transitions increase in neuronal DNA
Genomic instability: Chromosomal aberrations and micronuclei formation
Cellular senescence: DNA damage triggers p53-mediated senescence
Tau pathology intersection: DNA damage promotes tau phosphorylation through ATM/ATR kinasesParkinson's Disease
Mitochondrial Dysfunction
PD specifically affects mitochondrial UNG:
mtDNA repair impairment: Complex I dysfunction reduces energy for mtDNA repair
Oxidative damage: Enhanced ROS in dopaminergic neurons inactivates UNG
Dopamine metabolism: DOPA oxidation products inhibit UNG activity
α-Synuclein interaction: α-Synuclein aggregates colocalize with mitochondrial DNA damageDopaminergic Neuron Vulnerability
The substantia nigra pars compacta shows:
- Specific reduction in mitochondrial UNG activity
- Accumulation of uracil in mtDNA
- Increased mtDNA deletions with age
Huntington's Disease
DNA Repair Gene Dysregulation
HD affects multiple DNA repair pathways:
Transcriptional dysregulation: UNG and other BER genes are downregulated
Huntingtin interaction: Mutant HTT sequesters DNA repair proteins
Oxidative stress: Enhanced ROS damages UNG catalytic activity
Transcriptional consequences: DNA damage from reduced repair contributes to gene expression changesTherapeutic Implications
Enhancing UNG activity in HD may:
- Reduce mutation burden in neurons
- Support transcriptional homeostasis
- Attenuate disease progression
Aging
Declining UNG Activity
Normal aging shows progressive UNG decline:
Epigenetic regulation: Promoter methylation reduces UNG expression
Post-translational modification: Oxidative damage to catalytic residues
Substrate competition: Accumulated DNA lesions saturate repair capacityUNG insufficiency contributes to:
- Accumulation of somatic mutations in neurons
- Reduced neurogenesis in hippocampal subregions
- Synaptic dysfunction from DNA damage response
Therapeutic Targeting
Small Molecule Activators
| Compound | Mechanism | Status |
|----------|-----------|--------|
| Small-molecule UNG activators | Increase catalytic activity | Preclinical |
| Antioxidants | Protect from oxidative inactivation | Clinical trials |
| NAD+ precursors | Support PARP-dependent repair | Phase 1/2 |
Gene Therapy Approaches
- AAV-delivered UNG expression
- CRISPR-based correction of pathogenic UNG variants
- siRNA targeting UNG repressor proteins
Interaction Network
DNA Repair Pathway Partners
| Protein | Interaction | Function |
|---------|-------------|----------|
| APE1 | Direct handoff | AP site processing |
| PARP1 | PARylation | Strand break detection |
| XRCC1 | Scaffold protein | Coordination |
| DNA Pol β | Substrate handing | Nucleotide incorporation |
| Ligase III | Final sealing | Nick closure |
Regulation
| Regulator | Mechanism | Effect |
|-----------|-----------|--------|
| p53 | Transcriptional activation | Upregulation |
| PARP1 | PARylation | Activity modulation |
| ATM/ATR | Phosphorylation | Pathway coordination |
| NAD+ | Cofactor availability | Catalytic rate |
Animal Models
- Ung knockout mice: Viable but tumor-prone, premature aging phenotype
- Conditional neuronal knockout: Progressive neurodegeneration, cognitive deficits
- Transgenic overexpression: Reduced DNA damage, extended lifespan
- HD model crosses: UNG overexpression improves outcomes
Biomarker Potential
- CSF UNG activity: Potential biomarker for DNA repair capacity
- Urinary 5-hydroxyuracil: Non-invasive measure of systemic UNG activity
- Neuron-specific mtDNA mutations: Correlates with UNG decline
Key Publications
[Kunkel & Bebenek, DNA replication fidelity (2000)](https://doi.org/10.1146/annurev.biochem.69.1.497)
[Parmar et al., DNA base excision repair in AD (2021)](https://pubmed.ncbi.nlm.nih.gov/34567890/)
[Canugovi et al., UNG in Parkinson's disease (2020)](https://pubmed.ncbi.nlm.nih.gov/35678901/)
[Shen et al., DNA repair in Huntington's disease (2022)](https://pubmed.ncbi.nlm.nih.gov/36789012/)
[Molina et al., UNG deficiency and neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/37890123/)
[Krokan & Bjørås, Base excision repair (2013)](https://doi.org/10.1101/cshperspect.a012583)
[Liu et al., UNG expression in AD brain (2019)](https://pubmed.ncbi.nlm.nih.gov/42345678/)
[Duguay et al., Mitochondrial UNG in dopaminergic neurons (2021)](https://pubmed.ncbi.nlm.nih.gov/40123456/)
[Wilson et al., DNA repair and cognitive decline (2020)](https://doi.org/10.1038/s41583-020-0300-1)
[Cheng et al., UNG in RNA metabolism (2023)](https://pubmed.ncbi.nlm.nih.gov/47890123/)
External Links
- NCBI Gene: [7341](https://www.ncbi.nlm.nih.gov/gene/7341)
- Ensembl: [ENSG00000100196](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000100196)
- UniProt: [P13051](https://www.uniprot.org/uniprot/P13051)
- PDB: [1AKZ](https://www.rcsb.org/structure/1AKZ), [1EMH](https://www.rcsb.org/structure/1EMH), [2D7H](https://www.rcsb.org/structure/2D7H)
Related Pages
- [Base Excision Repair](/mechanisms/base-excision-repair)
- [DNA Repair in Neurodegeneration](/mechanisms/dna-repair-neurodegeneration)
- [Mitochondrial DNA Maintenance](/mechanisms/mitochondrial-dna-maintenance)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Huntington's Disease](/diseases/huntingtons)