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Watching right and wrong nucleotide insertion captures hidden polymerase fidelity checkpoints.

Joonas A Jamsen1, David D Shock2, Samuel H Wilson3

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|June 10, 2022
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Summary

DNA polymerase fidelity checkpoints ensure accurate DNA synthesis. This study reveals how polymerase lambda (pol λ) uses active site deformation and metal ions to distinguish correct from incorrect nucleotide insertion, maintaining genomic stability.

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Area of Science:

  • Molecular Biology
  • Biochemistry
  • Genetics

Background:

  • DNA polymerase fidelity checkpoints are crucial for accurate DNA synthesis.
  • X-family polymerase lambda (pol λ) errors contribute to genomic instability during DNA repair.
  • Understanding pol λ's nucleotide insertion mechanism is key to genomic stability.

Purpose of the Study:

  • To elucidate the intermediate catalytic states and nucleotide sensing mechanisms of pol λ.
  • To investigate how pol λ distinguishes between correct and incorrect nucleotide insertion.
  • To uncover the role of active site metals in pol λ fidelity.

Main Methods:

  • Time-lapse crystallography to capture intermediate catalytic states.
  • Analysis of nucleotide insertion dynamics (right vs. wrong).
  • Investigation of active site metal ion roles.

Main Results:

  • Pol λ utilizes active site deformation to sense base pair geometry and align the polymerase-substrate complex.
  • An induced fit mechanism differentiates correct from incorrect nucleotide insertion.
  • A third active site metal accelerates correct insertion but is not essential for synthesis.

Conclusions:

  • Fidelity checkpoints in pol λ involve dynamic responses to nucleotide geometry.
  • These mechanisms regulate distinct reaction pathways for accurate DNA repair synthesis.
  • Uncovered checkpoints offer insights into preventing genomic instability.