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Updated: Apr 23, 2026
Single-Molecule Fluorescence Visualization of DNA Polymerase Dynamics at G-Quadruplexes
Published on: April 4, 2025
Mechanism of suppression of chromosomal instability by DNA polymerase POLQ
Matthew J Yousefzadeh1, David W Wyatt2, Kei-Ichi Takata1
1Department of Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Smithville, Texas, United States of America; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas, United States of America.
Abstract:
Although a defect in the DNA polymerase POLQ leads to ionizing radiation sensitivity in mammalian cells, the relevant enzymatic pathway has not been identified. Here we define the specific mechanism by which POLQ restricts harmful DNA instability. Our experiments show that Polq-null murine cells are selectively hypersensitive to DNA strand breaking agents, and that damage resistance requires the DNA polymerase activity of POLQ. Using a DNA break end joining assay in cells, we monitored repair of DNA ends with long 3' single-stranded overhangs. End joining events retaining much of the overhang were dependent on POLQ, and independent of Ku70. To analyze the repair function in more detail, we examined immunoglobulin class switch joining between DNA segments in antibody genes. POLQ participates in end joining of a DNA break during immunoglobulin class-switching, producing insertions of base pairs at the joins with homology to IgH switch-region sequences. Biochemical experiments with purified human POLQ protein revealed the mechanism generating the insertions during DNA end joining, relying on the unique ability of POLQ to extend DNA from minimally paired primers. DNA breaks at the IgH locus can sometimes join with breaks in Myc, creating a chromosome translocation. We found a marked increase in Myc/IgH translocations in Polq-defective mice, showing that POLQ suppresses genomic instability and genome rearrangements originating at DNA double-strand breaks. This work clearly defines a role and mechanism for mammalian POLQ in an alternative end joining pathway that suppresses the formation of chromosomal translocations. Our findings depart from the prevailing view that alternative end joining processes are generically translocation-prone.
Insights
DNA polymerase POLQ (Polynucleotide phosphorylase-like Q) activity is crucial for repairing DNA strand breaks and preventing genomic instability in mammalian cells. This study reveals POLQ
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- A defect in DNA polymerase POLQ (Polynucleotide phosphorylase-like Q) causes ionizing radiation sensitivity in mammalian cells.
- The specific enzymatic pathway by which POLQ mitigates DNA instability remained unidentified.
- Understanding POLQ's role is critical for comprehending DNA repair mechanisms and genomic stability.
Purpose of the Study:
- To elucidate the precise mechanism by which DNA polymerase POLQ (Polynucleotide phosphorylase-like Q) prevents harmful DNA instability.
- To define POLQ's role in DNA double-strand break repair and its impact on genomic rearrangements.
- To investigate the biochemical function of POLQ in DNA end joining pathways.
Main Methods:
- Utilized Polq-null murine cells to assess sensitivity to DNA strand breaking agents.
- Employed a DNA break end joining assay to monitor the repair of DNA ends with long 3' single-stranded overhangs.
- Conducted biochemical experiments with purified human POLQ protein to determine its enzymatic mechanism.
Main Results:
- Polq-null murine cells exhibited hypersensitivity to DNA strand breaking agents, requiring POLQ's polymerase activity for damage resistance.
- POLQ was essential for end joining events retaining long 3' single-stranded overhangs, independent of Ku70.
- POLQ participates in immunoglobulin class switch joining, generating insertions at DNA joins, and suppresses Myc/IgH translocations.
Conclusions:
- Mammalian DNA polymerase POLQ plays a defined role in an alternative end joining pathway that suppresses chromosomal translocations.
- POLQ's unique ability to extend DNA from minimally paired primers underlies its function in DNA end joining.
- This research clarifies POLQ's mechanism in preventing genomic instability and challenges the view that alternative end joining is inherently translocation-prone.
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