A solution to release twisted DNA during chromosome replication by coupled DNA polymerases

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• DNA replication requires coordinated actions of leading and lagging strand polymerases.
• Coupled replication presents topological challenges due to DNA's helical structure, leading to supercoil buildup.
• The mechanism by which polymerases maintain connection despite these challenges is poorly understood.

Purpose of the Study:

• To investigate the dynamics of the Escherichia coli replisome.
• To elucidate how DNA polymerases maintain connection during coupled replication.
• To understand the resolution of topological problems during DNA synthesis.

Main Methods:

• Ensemble biochemical assays.
• Single-molecule biophysical techniques.
• Analysis of replisome dynamics in Escherichia coli.

Main Results:

• The lagging-strand polymerase frequently dissociates from Okazaki fragments before completion, creating transient gaps.
• This 'signal release' is independent of primase and does not require a protein trigger.
• Lagging-strand polymerase exhibits reduced processivity within the replisome, which is restored when uncoupled.

Conclusions:

• The replisome manages topological stress through transient dissociation of the lagging-strand polymerase.
• Accumulated superhelical tension in newly synthesized DNA likely reduces lagging-strand polymerase processivity.
• This mechanism allows for efficient DNA replication without relying on topoisomerases to resolve topological issues.