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Related Experiment Video

Updated: Aug 10, 2025

Single-Molecule Fluorescence Visualization of DNA Polymerase Dynamics at G-Quadruplexes
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DNA Base Excision Repair Intermediates Influence Duplex-Quadruplex Equilibrium.

Mark L Sowers1,2, James W Conrad1, Bruce Chang-Gu1,2

  • 1Department of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USA.

Molecules (Basel, Switzerland)
|February 11, 2023
PubMed
Summary
This summary is machine-generated.

DNA damage and base excision repair (BER) enzymes impact G-quadruplex structures. BER enzyme activity is inhibited by DNA damage within G-quadruplexes, affecting DNA repair efficiency.

Keywords:
DNA quadruplexbase excision repairduplex-quadruplex equilibriumglycosylasepyridostatintelomere

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Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • Genomic DNA typically exists as a duplex but can form alternative structures like G-quadruplexes.
  • G-quadruplexes are found in gene promoters, telomeres, and cancer-associated genomic regions.
  • Base excision repair (BER) pathway repairs endogenous DNA damage in duplex DNA, but its function in non-duplex structures is less understood.

Purpose of the Study:

  • To investigate the effects of DNA damage and repair intermediates on G-quadruplex structure and BER enzyme activity.
  • To understand how DNA damage and repair influence the equilibrium between duplex and G-quadruplex DNA.

Main Methods:

  • Incorporation of pyrimidine damage products (uracil, 5-hydroxymethyluracil, 5-fluorouracil, abasic site) into G-quadruplex loop regions.
  • Assessing the impact of these modifications on G-quadruplex formation and BER enzyme (UDG, SMUG1, APE1) activity.
  • Studying the effect of DNA repair intermediates in the strand opposite the G-quadruplex on duplex-quadruplex equilibrium.

Main Results:

  • G-quadruplex formation was not affected by the presence of uracil analogs or abasic sites in the loop.
  • Uracil DNA glycosylase (UDG), SMUG1, and APE1 activities were significantly inhibited by DNA damage within the G-quadruplex.
  • DNA repair intermediates in the opposing strand destabilized duplex DNA and promoted G-quadruplex formation.
  • A G-quadruplex stabilizing molecule (pyridostatin) promoted G-quadruplex formation from duplex DNA.

Conclusions:

  • DNA damage and repair intermediates can alter the dynamic equilibrium between duplex and G-quadruplex DNA structures.
  • BER enzyme efficiency is compromised when DNA damage occurs within G-quadruplex structures.
  • These findings highlight the complex interplay between DNA structure, damage, and repair in the genome.