Factors affecting template switch recombination associated with restarted DNA replication.

Area of Science:

• Molecular Biology
• Genetics
• DNA Replication and Repair

Background:

• Homologous recombination (HR) is crucial for restarting collapsed replication forks during genome duplication.
• Replication restart mediated by HR can lead to template switching (TS), a process that generates detrimental genome rearrangements implicated in diseases like cancer.
• An established assay in *Schizosaccharomyces pombe* allows for the study of TS.

Purpose of the Study:

• To investigate the distance downstream of a collapsed replication fork where TS can be detected.
• To identify factors that trigger TS during replication restart.
• To determine the role of specific DNA helicases in suppressing TS.

Main Methods:

• Utilized a previously established assay in *Schizosaccharomyces pombe* to detect and quantify template switching.
• Investigated TS frequency in the vicinity of collapsed replication forks and in proximity to RNA Polymerase III transcription.
• Assessed the impact of mutations in conserved DNA helicases (Pif1/Pfh1, Fbh1, Rqh1, Srs2) and other factors (Fml1, Mus81) on TS frequency.

Main Results:

• Template switching (TS) was detected up to 75 kb downstream of a collapsed replication fork.
• Head-on collisions between restarted replication forks and RNA Polymerase III transcription were identified as triggers for TS.
• The Pif1 DNA helicase (Pfh1) was found to promote efficient fork restart and suppress TS.
• Fbh1, Rqh1, and Srs2 helicases significantly suppressed TS, while Fml1 and Mus81 showed no effect on TS frequency.

Conclusions:

• Replication restart is susceptible to template switching (TS) over considerable distances and can be exacerbated by transcriptional interference.
• Conserved DNA helicases, particularly Pfh1, Fbh1, Rqh1, and Srs2, play critical roles in suppressing TS and maintaining genome stability.
• Understanding the mechanisms of TS suppression is vital for preventing disease-associated genome rearrangements.