Swi1 prevents replication fork collapse and controls checkpoint kinase Cds1

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• The replication checkpoint safeguards genome integrity by stabilizing stalled replication forks and arresting cell division.
• In budding yeast, Tof1 mediates the replication checkpoint signal activating Rad53.
• Fission yeast Swi1, a Tof1 homolog, is essential for programmed fork pausing during mating type switching.

Purpose of the Study:

• To investigate the role of fission yeast Swi1 in replication checkpoint activation and fork stability.
• To elucidate the relationship between Swi1, Cds1, and DNA repair pathways.
• To understand the mechanisms by which Swi1 prevents replication fork collapse and irreversible arrest.

Main Methods:

• Genetic analysis of fission yeast mutants (swi1, cds1).
• Assessment of replication fork stability using DNA repair foci (Rad22) and endonuclease requirements (Mus81).
• Chromatin recruitment studies of Swi1 during S phase.

Main Results:

• Swi1 is vital for the activation of the Cds1 checkpoint kinase.
• Swi1 and Cds1 prevent fork collapse in ribosomal DNA repeats and at hydroxyurea-induced pause sites.
• Swi1 exhibits Cds1-independent functions, including preventing fork collapse and requiring Mus81 for recovery, suggesting its direct role in fork stabilization.

Conclusions:

• Swi1 plays a critical role in activating the Cds1-mediated replication checkpoint.
• Swi1 is essential for preventing replication fork collapse and irreversible arrest, thereby maintaining genome integrity.
• Swi1 likely stabilizes replication forks, facilitating their recognition by checkpoint sensors.