DNA polymerase δ proofreads errors made by DNA polymerase ε

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Eukaryotic DNA replication involves DNA Polymerase ε (Polε) and DNA Polymerase δ (Polδ) synthesizing leading and lagging strands.
• A long-standing paradox exists where Polε fidelity defects have a weaker impact on mutagenesis than Polδ defects.

Purpose of the Study:

• To provide direct evidence for the proposed model that Polδ proofreads errors made by Polε.
• To investigate the directionality of proofreading between Polε and Polδ.

Main Methods:

• Yeast genetics to combine nucleotide selectivity and proofreading defects in Polε and Polδ.
• In vitro assays to assess Polδ's ability to remove errors from exonuclease-deficient Polε.

Main Results:

• Synergistic increase in mutation rate when combining Polε selectivity and Polδ proofreading defects, confirming Polδ proofreads Polε errors.
• No synergistic effect when combining Polδ selectivity and Polε proofreading defects, indicating Polε does not proofread Polδ errors.
• Polδ demonstrated the ability to remove errors made by exonuclease-deficient Polε in vitro.

Conclusions:

• DNA Polymerase δ provides extrinsic proofreading for errors made by DNA Polymerase ε.
• This finding challenges the strict one-strand-one-polymerase model, revealing a more complex proofreading mechanism where Polδ proofreading extends to both DNA strands.