High-accuracy lagging-strand DNA replication mediated by DNA polymerase dissociation

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• DNA replication fidelity is crucial for preventing mutations.
• Antiparallel DNA strands are replicated differently: leading strand continuously, lagging strand discontinuously (Okazaki fragments).
• Previous studies faced challenges in comparing strand fidelity due to different polymerases used for each strand in eukaryotes.

Purpose of the Study:

• To determine if DNA replication occurs with the same intrinsic fidelity on both the leading and lagging strands.
• To investigate strand-specific replication accuracy in *Escherichia coli*.

Main Methods:

• Utilized *in vivo* mutagenesis assays in *Escherichia coli*.
• Exploited the unique characteristic of *E. coli*'s DNA polymerase III holoenzyme, which uses the same polymerase (Pol III, encoded by *dnaE*) for both strands.
• Examined the impact of *dnaE* antimutator polymerases with altered dissociation rates.

Main Results:

• Demonstrated that DNA replication fidelity is not equal between the two strands in *E. coli*.
• Revealed that the lagging strand exhibits significantly higher fidelity compared to the leading strand.
• Observed that increased polymerase dissociation rates, seen in *dnaE* antimutator mutants, correlate with higher fidelity.

Conclusions:

• The lagging strand of DNA is replicated with higher intrinsic fidelity than the leading strand.
• Postulated that the lagging-strand polymerase's greater dissociative character enhances error removal mechanisms.
• Findings provide insights into the regulation of DNA replication accuracy and mutation rates.