A single unbranched S-phase DNA damage and replication fork blockage checkpoint pathway

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• The eukaryotic intra-S-phase checkpoint regulates DNA synthesis during replication stress.
• The precise mechanisms of DNA damage recognition and checkpoint activation remain unclear.
• Potential roles of competition between DNA synthesis and repair pathways are debated.

Purpose of the Study:

• To investigate the mechanisms underlying the intra-S-phase checkpoint in fission yeast, Schizosaccharomyces pombe.
• To determine whether DNA damage is recognized directly or indirectly via replication fork effects.
• To assess the contribution of recombination/repair pathways to S-phase slowing.

Main Methods:

• Genetic analyses in Schizosaccharomyces pombe.
• Evaluation of the roles of specific helicases (Rqh1, Srs2) and recombination/repair proteins.
• Assessment of checkpoint protein dependencies (checkpoint-Rad proteins, Cds1, Rad4/Cut5, Rhp9).

Main Results:

• Slowing of S phase showed weak dependence on helicases Rqh1 and Srs2.
• Other recombination/repair pathways were not essential for S-phase slowing.
• Strong dependence on checkpoint proteins (checkpoint-Rad, Cds1, Rad4/Cut5) was observed.
• Rhp9, implicated in direct damage recognition in other yeasts, was not essential.

Conclusions:

• In fission yeast, the intra-S-phase checkpoint signal is generated specifically when replication forks encounter DNA damage.
• Direct DNA damage recognition is unlikely to be the primary trigger for this checkpoint in S. pombe.
• The findings highlight the importance of replication fork integrity in checkpoint activation.