Strand Displacement Increases the Fidelity of DNA Polymerases

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• DNA polymerase fidelity is crucial for genome stability.
• Previous studies often used simplified substrates, neglecting complex DNA structures.
• Strand displacement synthesis is a common process in DNA replication and repair.

Purpose of the Study:

• To evaluate the fidelity of Klenow fragment (KF) and RB69 DNA polymerase (RBpol) during strand displacement synthesis.
• To investigate how the presence of a downstream strand affects DNA polymerase fidelity.
• To determine the impact of base pair strength on polymerase fidelity.

Main Methods:

• Assessing single deoxynucleotide monophosphate (dNMP) incorporation fidelity.
• Utilizing primer-template substrates with varying base pair strengths (mismatches, synthetic analogs).
• Comparing fidelity in standard primer-template systems versus strand displacement scenarios.

Main Results:

• Both KF and RBpol exhibited significantly higher fidelity (3-fold to 10-fold increase) during strand displacement compared to primer-template systems.
• Polymerase efficiency often decreased as fidelity increased.
• Stronger base pairs ahead of the incorporation site led to higher fidelity for both polymerases.

Conclusions:

• The downstream strand in strand displacement synthesis acts as a fidelity checkpoint.
• This checkpoint enhances discrimination against incorrect nucleotides, thereby improving genome stability.
• DNA polymerases can trade efficiency for fidelity, particularly when encountering stronger base pairs.