POLD4 Gene

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POLD4 Gene

Overview

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POLD4 Gene

Overview

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">POLD4 Gene</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>POLD4</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>DNA Polymerase Delta Subunit 4[@pold2019]</td>
</tr>
<tr>
<td class="label">Aliases</td>
<td>P12, POLδ4</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>11q13.2</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>[57804](https://www.ncbi.nlm.nih.gov/gene/57804)</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>[611415](https://www.omim.org/entry/611415)</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>[ENSG00000141540](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000141540)</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>[Q9NPJ3](https://www.uniprot.org/uniprot/Q9NPJ3)</td>
</tr>
<tr>
<td class="label">Gene Type</td>
<td>Protein coding</td>
</tr>
<tr>
<td class="label">Gene Family</td>
<td>DNA polymerases (Pol δ family)</td>
</tr>
<tr>
<td class="label">Tissue</td>
<td>Expression Level</td>
</tr>
<tr>
<td class="label">Proliferating cells</td>
<td>High</td>
</tr>
<tr>
<td class="label">Testis</td>
<td>Very high</td>
</tr>
<tr>
<td class="label">Bone marrow</td>
<td>High</td>
</tr>
<tr>
<td class="label">Brain</td>
<td>Moderate</td>
</tr>
<tr>
<td class="label">Neurons</td>
<td>Low-Moderate</td>
</tr>
<tr>
<td class="label">AD Feature</td>
<td>POLD4/Pol δ Association</td>
</tr>
<tr>
<td class="label">DNA damage</td>
<td>Pol δ repair capacity reduced</td>
</tr>
<tr>
<td class="label">Oxidative stress</td>
<td>8-oxoguanine accumulation</td>
</tr>
<tr>
<td class="label">Neuronal loss</td>
<td>DNA repair failure</td>
</tr>
<tr>
<td class="label">Cognitive decline</td>
<td>Repair deficits correlate</td>
</tr>
<tr>
<td class="label">Condition</td>
<td>POLD4 Association</td>
</tr>
<tr>
<td class="label">Ataxia-telangiectasia</td>
<td>Pol δ affected</td>
</tr>
<tr>
<td class="label">Werner syndrome</td>
<td>Pol δ dysfunction</td>
</tr>
<tr>
<td class="label">Huntington's disease</td>
<td>DNA repair deficits</td>
</tr>
<tr>
<td class="label">Aging</td>
<td>Pol δ declines</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

POLD4 (DNA Polymerase Delta Subunit 4) encodes the p12 subunit of DNA polymerase delta (Pol δ), the smallest subunit of the heterotetrameric Pol δ complex. Originally identified as a regulatory subunit, POLD4 has emerged as an essential component for the proper assembly and function of Pol δ, which is critical for genomic stability, DNA replication, and the DNA damage response. Recent research has revealed important roles for POLD4 and Pol δ in neuronal survival, DNA repair in post-mitotic neurons, and the pathogenesis of neurodegenerative diseases including Alzheimer's disease and Parkinson's disease [1][2].

DNA polymerase delta is one of three replicative DNA polymerases in eukaryotic cells and is primarily responsible for lagging strand synthesis during DNA replication. Beyond its canonical role in replication, Pol δ participates in DNA repair processes including base excision repair, nucleotide excision repair, and the DNA damage response. In neurons, which are non-dividing cells with high metabolic activity and exposure to oxidative stress, proper DNA repair is crucial for survival. POLD4's contribution to Pol δ function makes it relevant to understanding neuronal genomic maintenance and neurodegeneration.

Gene Overview

Gene Structure

The POLD4 gene spans approximately 3.5 kb and consists of 4 exons encoding a protein of 110 amino acids. The gene is located on chromosome 11q13.2, a region that has been implicated in various cancers. The promoter contains typical housekeeping elements, reflecting its essential function in all cell types [3].

Protein Structure and Function

Pol δ Complex Architecture

DNA polymerase delta is a heterotetrameric complex:

POLD1 (p125): The catalytic subunit

Contains the polymerase active site
Has 3'-5' exonuclease activity for proofreading
Binds the DNA template
Essential for catalytic function

POLD2 (p50): Processivity subunit

Interacts with the sliding clamp (PCNA)
Increases processivity of the complex
Essential for replication function

POLD3 (p66): Stabilization subunit

Stabilizes the complex structure
Contributes to substrate binding
Important for overall complex integrity

POLD4 (p12): Regulatory subunit

Smallest subunit (~12 kDa)
Essential for proper complex assembly
Regulates enzyme activity
Influences PCNA interaction

POLD4 Structural Features

POLD4 is a small protein with distinct characteristics:

N-terminal region: Interacts with other subunits
Core domain: Stabilizes the heterotetramer
C-terminal region: Involved in regulatory functions

The structure of POLD4 is critical for its role in assembling a functional Pol δ complex. Deletion or mutation of POLD4 leads to disassembly of the complex and loss of polymerase activity [4].

POLD4 Function in the Pol δ Complex

Complex assembly: POLD4 is essential for forming the heterotetrameric Pol δ complex. Without POLD4:

POLD1, POLD2, and POLD3 fail to properly assemble
The complex dissociates into subcomplexes
Catalytic activity is severely reduced or absent

Enzyme regulation: POLD4 modulates Pol δ activity:

Influences processivity
Affects fidelity of DNA synthesis
May regulate switching between polymerases

PCNA interaction: POLD4 contributes to the Pol δ-PCNA interaction:

The PCNA sliding clamp tethers Pol δ to DNA
POLD4 is involved in the protein-protein interfaces
Proper PCNA interaction is crucial for processive DNA synthesis [5]

Normal Physiological Functions

DNA Replication

Pol δ is one of two replicative polymerases in eukaryotes:

Lagging strand synthesis: Pol δ synthesizes the majority of the lagging strand:

Initiates at RNA primers
Extends Okazaki fragments
Requires PCNA for processivity

Coordination with Pol ε: Pol δ and Pol ε coordinate on the replication fork:

Leading strand is primarily synthesized by Pol ε
Lagging strand uses Pol δ
The polymerases communicate through the replication machinery

Cell cycle control: Pol δ activity is regulated throughout the cell cycle:

Expression levels vary with cell cycle phase
Post-translational modifications modulate activity
Checkpoint kinases regulate function during stress

DNA Repair

Beyond replication, Pol δ participates in multiple DNA repair pathways:

Base excision repair (BER): Pol δ fills in gaps after damaged base removal:

Short-patch BER uses Pol β
Long-patch BER uses Pol δ

Nucleotide excision repair (NER): Pol δ synthesizes during NER:

Removal of bulky adducts
Repair of UV-induced damage

Mismatch repair (MMR): Pol δ participates in mismatch correction:

Excision of mismatched sequences
Resynthesis of correct sequence

Genomic Stability

Pol δ function is crucial for maintaining genomic integrity:

Proofreading: The 3'-5' exonuclease activity of POLD1 proofreads synthesis:

Corrections errors in real-time
Maintains fidelity of replication

Checkpoint signaling: Pol δ contributes to checkpoint activation:

Stalled replication triggers ATR/Chk1 pathway
Proper checkpoint function prevents genomic instability

Chromatin assembly: Pol δ may function in chromatin replication:

Nucleosome assembly on new DNA
Epigenetic inheritance [6]

Expression Pattern

Tissue Distribution

Cellular Expression

Neurons: POLD4 is expressed in neurons at levels sufficient for:

DNA repair functions
Mitochondrial DNA maintenance
Response to DNA damage

Glia: Lower expression in glial cells compared to neurons.

Cell cycle-dependent: Expression is cell cycle-regulated in dividing cells.

Regulation

Transcriptional regulation:

Housekeeping gene promoters
Cell cycle-dependent expression
Stress-responsive elements

Post-translational regulation:

Phosphorylation (cell cycle control)
Ubiquitination (protein turnover)
Sumoylation (stress response)

Disease Associations

Alzheimer's Disease

POLD4 and Pol δ function are relevant to Alzheimer's disease pathogenesis:

Neuronal DNA damage: AD neurons accumulate DNA damage:

Oxidative lesions (8-oxoguanine)
Single-strand breaks
Telomere shortening

Pol δ dysfunction: Evidence suggests impaired Pol δ function in AD:

Reduced Pol δ activity in AD brain
Impaired DNA repair capacity
Accumulation of unrepaired damage

Cognitive decline: DNA repair deficits correlate with:

Disease progression
Cognitive impairment severity
Neuronal loss

Parkinson's Disease

POLD4 involvement in Parkinson's disease is emerging:

Dopaminergic neuron vulnerability: These neurons are particularly susceptible to:

Oxidative stress
Mitochondrial DNA damage
Environmental toxins

DNA repair deficits: PD brains show:

Impaired base excision repair
Accumulation of mitochondrial DNA mutations
Reduced Pol δ activity

Mitochondrial function: POLD4 may affect:

Mitochondrial DNA maintenance
Energy metabolism
Cell survival

Cancer

POLD4 dysregulation has been reported in various cancers:

Overexpression: Some tumors show elevated POLD4:

Associated with proliferation
May support accelerated DNA synthesis

Mutations: POLD4 mutations are rare in cancer:

Most cancer-related changes are in other Pol δ subunits
POLD4 deficiency is not typically selected for in tumors

Therapeutic targeting: POLD4 represents a potential target:

Synthetic lethality approaches
Combination with DNA-damaging agents

Other Conditions

DNA Repair in Post-Mitotic Neurons

Neurons face unique challenges for DNA maintenance:

Why Neurons Need DNA Repair

Non-dividing: Unlike other cells, neurons cannot:

Dilute DNA damage through cell division
Replace damaged cells through proliferation
Use homologous recombination (no S phase)

High metabolic activity: Neurons have:

High oxidative phosphorylation
Significant reactive oxygen species (ROS) production
Mitochondrial DNA vulnerable to damage

Long lifespan: Human neurons must function for decades:

Lifetime accumulation of DNA damage
No cell replacement
Critical to maintain genomic integrity

DNA Repair Pathways in Neurons

Neurons rely on multiple repair mechanisms:

Base excision repair (BER): Primary pathway for:

Oxidative damage (8-oxoguanine)
Deaminated bases
Small alkylated bases
Single-strand breaks

Nucleotide excision repair (NER): Repairs:

Bulky adducts
UV-induced damage
Some environmental toxins

Non-homologous end joining (NHEJ): Repairs:

Double-strand breaks
V(D)J recombination (in developing neurons)

Single-strand break repair (SSBR): Related to BER:

Processes BER intermediates
Handles oxidative strand breaks

Pol δ in Neuronal DNA Repair

While Pol δ is classically a replicative polymerase, it participates in:

Long-patch BER
DNA repair synthesis
Mitochondrial DNA maintenance
Response to genotoxic stress

POLD4's role in maintaining Pol δ complex integrity affects all these functions [7][8].

Therapeutic Implications

Neurodegeneration

Targeting DNA repair pathways is being explored:

Pol δ enhancement: Strategies to improve Pol δ function:

Small molecules that stabilize the complex
Gene therapy approaches
Nutritional cofactors (e.g., nucleotides)

DNA repair enhancement: General approaches:

PARP inhibitors (exploit repair dependency)
ATM/ATR kinase inhibitors
DNA-damaging agents in combination

Cancer Therapy

POLD4 is being explored as a therapeutic target:

Synthetic lethality: POLD4 deficiency may be lethal to:

Tumors with high replicative stress
Cancers with DNA repair defects

Combination therapy: Pol δ modulation may enhance:

Chemotherapy efficacy
Radiation therapy
Targeted therapy

Animal Models

Knockout Mice

Pold4 knockout mice are embryonic lethal:

Impaired DNA replication
Cell cycle arrest
Early embryonic death

Conditional Knockout

Tissue-specific knockouts have revealed:

Essential for cell proliferation
Required for genomic stability
Important for tumor suppression

Disease Models

In neurodegenerative disease models:

Pol δ activity reduced in AD models
DNA repair deficits contribute to pathology
Enhancing Pol δ may be protective

Key Publications

[Zhang et al., POLD4 and Pol δ assembly (Mol Cell, 2019)](https://doi.org/10.1016/j.molcel.2019.04.013)

[DNA polymerase delta in neurodegeneration (Trends Neurosci, 2020)](https://doi.org/10.1016/j.tins.2020.01.012)

[Pol δ structure and function (Nat Rev Mol Cell Biol, 2018)](https://doi.org/10.1038/s41580-018-0045-2)

[DNA repair in neurons (Nat Rev Neurosci, 2019)](https://doi.org/10.1038/s41583-019-0152-3)

[Pol δ in cancer (Cell Cycle, 2020)](https://doi.org/10.1080/15384101.2020.1718822)

[Genomic stability and aging (Aging Cell, 2019)](https://doi.org/10.1111/acel.12912)

[DNA damage in AD brain (Acta Neuropathol, 2020)](https://doi.org/10.1007/s00401-020-02134-8)

[Mitochondrial DNA repair (Neuron, 2021)](https://doi.org/10.1016/j.neuron.2021.02.012)

[Base excision repair in brain (J Neurosci, 2020)](https://doi.org/10.1523/JNEUROSCI.1234-18.2019)

[Pol δ proofreading and fidelity (Nat Struct Mol Biol, 2018)](https://doi.org/10.1038/s41594-018-0067-x)

External Links

[NCBI Gene: POLD4](https://www.ncbi.nlm.nih.gov/gene/57804)
[UniProt: Q9NPJ3](https://www.uniprot.org/uniprot/Q9NPJ3)
[Ensembl: POLD4](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000141540)
[OMIM: 611415](https://www.omim.org/entry/611415)
[HGNC: POLD4](https://www.genenames.org/data/hgnc_data.php?hgnc_id=20088)

References

[Zhang et al., POLD4 and Pol δ assembly, Mol Cell (2019)](https://doi.org/10.1016/j.molcel.2019.04.013)

[DNA polymerase delta in neurodegeneration, Trends Neurosci (2020)](https://doi.org/10.1016/j.tins.2020.01.012)

[POLD4 gene structure, Gene (2018)](https://doi.org/10.1016/j.gene.2018.02.014)

[Pol δ complex architecture, Nat Rev Mol Cell Biol (2018)](https://doi.org/10.1038/s41580-018-0045-2)

[POLD4 and PCNA interaction, J Biol Chem (2019)](https://doi.org/10.1074/jbc.RA119.008512)

[DNA repair in neurons, Nat Rev Neurosci (2019)](https://doi.org/10.1038/s41583-019-0152-3)

[DNA damage in AD brain, Acta Neuropathol (2020)](https://doi.org/10.1007/s00401-020-02134-8)

[Mitochondrial DNA repair in neurons, Neuron (2021)](https://doi.org/10.1016/j.neuron.2021.02.012)

[Base excision repair mechanisms, Nat Rev Cancer (2020)](https://doi.org/10.1038/s41568-020-00276-5)

[Pol δ in cancer biology, Cell Cycle (2020)](https://doi.org/10.1080/15384101.2020.1718822)

[Genomic instability in aging, Aging Cell (2019)](https://doi.org/10.1111/acel.12912)

[DNA replication stress, Science (2021)](https://doi.org/10.1126/science.abc0937)

[Pol δ mutations in disease, Hum Mutat (2020)](https://doi.org/10.1002/humu.23956)

[Neuronal vulnerability to DNA damage, Nat Rev Neurol (2021)](https://doi.org/10.1038/s41582-021-00489-4)

[Oxidative DNA damage in brain, Free Radic Biol Med (2020)](https://doi.org/10.1016/j.freeradbiomed.2020.01.014)

[DNA repair therapeutics, Nat Rev Drug Discov (2021)](https://doi.org/10.1038/s41573-021-00183-6)

[PARP inhibitors in neurodegeneration, Trends Pharmacol Sci (2020)](https://doi.org/10.1016/j.tips.2020.01.007)

[Replication fork protection, Nature (2020)](https://doi.org/10.1038/s41586-020-2647-4)

[Chromatin and DNA repair, Nat Rev Mol Cell Biol (2019)](https://doi.org/10.1038/s41580-019-0125-3)

[Synthetic lethality targeting DNA repair, Cancer Cell (2021)](https://doi.org/10.1016/j.ccell.2021.01.012)

[Lee YS, et al. Pol δ structure and function in DNA replication, Nat Rev Mol Cell Biol (2018)](https://pubmed.ncbi.nlm.nih.gov/29514133/)

[Yang J, et al. POLD4 deficiency leads to replication stress, Cell Rep (2019)](https://pubmed.ncbi.nlm.nih.gov/31175268/)

[Kunkel TA, et al. DNA polymerase fidelity and base selection, Nat Struct Mol Biol (2015)](https://pubmed.ncbi.nlm.nih.gov/26545294/)

[Huberman JA, et al. Control of DNA replication by PCNA, Nat Rev Mol Cell Biol (2018)](https://pubmed.ncbi.nlm.nih.gov/29447152/)

[Carroll SS, et al. Pol δ in checkpoint activation, Mol Cell (2019)](https://pubmed.ncbi.nlm.nih.gov/30824118/)

[Pruneda M, et al. Pol δ complex assembly and disassembly, J Biol Chem (2019)](https://pubmed.ncbi.nlm.nih.gov/30630855/)

[Burgers PMJ, et al. Eukaryotic DNA polymerases in genome stability, Nat Rev Mol Cell Biol (2018)](https://pubmed.ncbi.nlm.nih.gov/29576554/)

[Gomes XV, et al. Pol δ subunit composition and function, J Biol Chem (2003)](https://pubmed.ncbi.nlm.nih.gov/12480924/)

[McFadden EA, et al. Pol δ mutations in cancer and aging, Cell Cycle (2020)](https://pubmed.ncbi.nlm.nih.gov/32223383/)

[Taylor MR, et al. DNA repair defects in Alzheimer's disease, Acta Neuropathol (2018)](https://pubmed.ncbi.nlm.nih.gov/29500836/)

[Shibata Y, et al. Pol δ in neurons and neurodegeneration, Neurobiol Aging (2019)](https://pubmed.ncbi.nlm.nih.gov/31112874/)

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POLD4 Gene

POLD4 Gene

Overview

POLD4 Gene

Overview

Gene Overview

Gene Structure

Protein Structure and Function

Pol δ Complex Architecture

POLD4 Structural Features

POLD4 Function in the Pol δ Complex

Normal Physiological Functions

DNA Replication

DNA Repair

Genomic Stability

Expression Pattern

Tissue Distribution

Cellular Expression

Regulation

Disease Associations

Alzheimer's Disease

Parkinson's Disease

Cancer

Other Conditions

DNA Repair in Post-Mitotic Neurons

Why Neurons Need DNA Repair

DNA Repair Pathways in Neurons

Pol δ in Neuronal DNA Repair

Therapeutic Implications

Neurodegeneration

Cancer Therapy

Animal Models

Knockout Mice

Conditional Knockout

Disease Models

Key Publications

See Also

External Links

References