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Proofreading01:31

Proofreading

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Synthesis of new DNA molecules is carried out by the enzyme DNA polymerase, which adds nucleotides on the daughter strand complementary to the template DNA strand. DNA polymerase has a higher affinity to add the correct base and ensures fidelity during DNA replication. Furthermore,  it exhibits proofreading activity during replication, using an exonuclease domain that cuts off incorrect nucleotides from the nascent DNA strand.
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Translesion (TLS) polymerases rescue stalled DNA polymerases at sites of damaged bases by replacing the replicative polymerase and installing a nucleotide across the damaged site. Doing so, TLS allows additional time for the cell to repair the damage before resuming regular DNA replication.
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The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of these sequences uses a strand from another as a template to synthesize DNA in an enzyme-catalyzed reaction. The final product is a novel amalgamation of the two substrates. To ensure an accurate recombination of sequences, HR is restricted to the S and G2 phases of the cell cycle. At these stages, the DNA has been replicated already and the...
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Overview of DNA Repair02:25

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In order to be passed through generations, genomic DNA must be undamaged and error-free. However, every day, DNA in a cell undergoes several thousand to a million damaging events by natural causes and external factors. Ionizing radiation such as UV rays, free radicals produced during cellular respiration, and hydrolytic damage from metabolic reactions can alter the structure of DNA. Damages caused include single-base alteration, base dimerization, chain breaks, and cross-linkage.
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Ubiquitylation of DNA polymerase β via atypical K27 chains signals a DNA damage response.

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Updated: Mar 1, 2026

Author Spotlight: High-Throughput Image-Based Quantification of Mitochondrial DNA Synthesis and Distribution
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DNA Polymerase Beta Participates in Mitochondrial DNA Repair.

P Sykora1,2, S Kanno3, M Akbari4

  • 1Laboratory of Molecular Gerontology, National Institute on Aging, Intramural Research Program, Baltimore, Maryland, USA.

Molecular and Cellular Biology
|June 1, 2017
PubMed
Summary

DNA polymerase beta (Polβ), a nuclear base excision repair protein, is found in mitochondria. Polβ is crucial for mitochondrial DNA maintenance and overall cell function.

Keywords:
DNA polymerase betaTFAMbase excision repairmitochondriamitochondrial DNA repairmitochondrial healthmutational studies

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Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • DNA polymerase beta (Polβ) is a key nuclear base excision repair (BER) protein.
  • The localization and function of Polβ within mitochondria were previously unknown.

Purpose of the Study:

  • To investigate the presence and role of Polβ in mammalian mitochondria.
  • To identify mitochondrial interactors of Polβ and assess its function in mtDNA maintenance and mitochondrial homeostasis.

Main Methods:

  • Subcellular fractionation to isolate mitochondrial protein extracts.
  • Co-immunoprecipitation and mass spectrometry to identify Polβ interactors.
  • Polβ knockout (KO) cell and mouse models to assess mtDNA damage and mitochondrial function.
  • Nucleotide incorporation assays to measure polymerase activity.

Main Results:

  • Polβ was detected in mitochondrial protein extracts from mammalian tissues and cells.
  • Polβ interacts with mitochondrial DNA maintenance proteins TWINKLE, SSBP1, and TFAM.
  • Polβ knockout resulted in increased mtDNA damage, reduced nucleotide incorporation, impaired metabolic parameters, and mitochondrial dysfunction.

Conclusions:

  • Polβ is a mitochondrial polymerase involved in mtDNA maintenance.
  • Polβ is essential for mitochondrial homeostasis and function.