Suppression of genome instability by redundant S-phase checkpoint pathways in Saccharomyces cerevisiae

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Cancer cells exhibit increased genome rearrangements, but the underlying defects remain unclear.
• The Saccharomyces cerevisiae replication checkpoint is implicated in suppressing spontaneous genome rearrangements.

Purpose of the Study:

• To investigate the role of the intra-S checkpoint in suppressing genome rearrangements.
• To identify specific genes and pathways involved in preventing DNA replication errors and subsequent genomic instability.

Main Methods:

• Utilized methyl methanesulfonate (MMS) to activate the intra-S checkpoint without affecting other DNA damage checkpoints.
• Assessed genome rearrangement rates in wild-type and mutant Saccharomyces cerevisiae strains, including those with defects in RAD24, SGS1, PDS1, RAD50-MRE11-XRS2, and RAD53.
• Analyzed synergistic interactions between mutations affecting different checkpoint branches.

Main Results:

• Low doses of MMS increased genome rearrangements, particularly in strains with intra-S checkpoint defects.
• Rearrangements included translocations and deletions with telomere additions.
• Mutations in RAD24, SGS1, PDS1, RAD50-MRE11-XRS2, and RAD53 showed synergistic effects on genome instability.
• Inactivating S-phase checkpoints led to massive increases (12,000-14,000-fold) in genome instability.

Conclusions:

• Spontaneous genome rearrangements arise from DNA replication errors.
• S-phase checkpoints, including the intra-S checkpoint, are crucial for suppressing replication-associated genome instability.
• There is significant redundancy among S-phase checkpoints, highlighting a robust system for maintaining genomic integrity.