Minimal Resection Takes Place during Break-Induced Replication Repair of Collapsed Replication Forks and Is...

Area of Science:

• Molecular Biology
• DNA Repair Mechanisms
• Cell Cycle Regulation

Background:

• Topoisomerase I (Top1) activity can lead to DNA breaks during replication.
• Protein-linked DNA nicks (PDNs) are common replication-associated DNA lesions.
• One-ended double-strand breaks (DSBs) can arise from PDNs during DNA replication.

Purpose of the Study:

• To investigate DNA resection at one-ended DSBs generated by Top1-mimicking damage during replication.
• To elucidate the role of strand invasion and heteroduplex formation in regulating resection.
• To understand how the break-induced replication (BIR) pathway handles Top1-generated breaks.

Main Methods:

• Induction of Top1-mimicking DNA damage.
• Analysis of DNA resection at one-ended DSBs.
• Manipulation of strand invasion and DNA synthesis rates (e.g., hydroxyurea treatment).

Main Results:

• Minimal DNA resection was observed at one-ended DSBs formed during replication.
• Extensive resection occurred only when strand invasion was abolished.
• Inhibition of DNA synthesis did not lead to extended resection, implicating strand invasion/heteroduplex formation in restraining resection.

Conclusions:

• The break-induced replication (BIR) pathway's resection is tightly regulated during S phase.
• Strand invasion and/or heteroduplex formation actively restrain resection at Top1-induced breaks.
• The BIR pathway is adapted to safely manage frequent, naturally occurring DNA breaks like those from Top1 activity.