Replisome structure suggests mechanism for continuous fork progression and post-replication repair.

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• For five decades, the mechanism of DNA replication encountering damaged DNA templates remained unclear.
• Early hypotheses suggested replication forks stall at DNA lesions, halting DNA polymerase activity.
• Later discoveries revealed replication machinery can bypass impediments, leading to gaps and breaks in newly synthesized DNA.

Purpose of the Study:

• To elucidate the mechanism by which DNA replication proceeds past damaged or nicked DNA templates.
• To understand the coordination of key replication proteins, including helicase, primase, and DNA polymerases.
• To provide a structural basis for how the replisome navigates and overcomes replication roadblocks.

Main Methods:

• Analysis of the recently determined structure of the bacteriophage T7 replisome.
• Comparative analysis of bacterial and eukaryotic replisome structures and functions.
• Integration of structural data with existing knowledge on translesion synthesis, fork reversal, and recombination repair.

Main Results:

• The T7 replisome structure reveals tight coupling between leading-strand DNA polymerase and lagging-strand helicase.
• This organization provides a framework for understanding how the replisome skips DNA lesions.
• Discontinuous DNA synthesis, resulting from lesion skipping, appears to be repaired post-replication in both bacterial and eukaryotic systems.

Conclusions:

• The structure of the T7 replisome offers a novel perspective on lesion skipping during DNA replication.
• The replisome's ability to bypass impediments is crucial for completing DNA synthesis despite template damage.
• Post-replication repair is a conserved mechanism for addressing discontinuities arising from replication past lesions.