How DNA secondary structures drive replication fork instability.

Area of Science:

• Molecular Biology
• Genetics
• Genomics

Background:

• DNA secondary structures (hairpins, G-quadruplexes, etc.) are common obstacles for replication forks.
• The precise mechanisms by which these structures destabilize replication forks are not fully understood.

Purpose of the Study:

• To propose a framework detailing the immediate consequences of replication forks encountering DNA secondary structures.
• To link DNA structure dynamics, strand geometry, and replisome behavior.

Main Methods:

• Review of existing literature on DNA replication and secondary structures.
• Integration of mechanisms connecting structure dynamics with fork responses.
• Analysis of outcomes based on affected DNA strand (leading/lagging) and structure timing.

Main Results:

• Leading strand structures impede CMG helicase, leading to single-stranded DNA (ssDNA) gaps and inhibiting DNA polymerase ε.
• Lagging strand structures inhibit DNA polymerase δ and impair Okazaki fragment maturation, causing ssDNA nicks or gaps.
• Immediate double-strand breaks (DSBs) are unlikely; strand-specific ssDNA gaps are the predominant outcome.

Conclusions:

• DNA secondary structures predominantly induce ssDNA gaps rather than immediate DSBs.
• These ssDNA gaps can be converted to DSBs later, contributing to genome instability.
• Replication protein A (RPA) and the replication checkpoint play crucial roles in managing fork stress and coordinating repair.