Mrc1 and Tof1 prevent fragility and instability at long CAG repeats by their fork stabilizing function

Area of Science:

• Molecular Biology
• Genetics
• DNA Replication

Background:

• DNA replication fork integrity is crucial for preventing genomic instability.
• Replication fork stabilizers, such as Mrc1 and Tof1, travel with the fork and maintain its stability.
• Expanded CAG repeats can stall replication forks, leading to trinucleotide expansion diseases.

Purpose of the Study:

• To investigate the roles of Mrc1 and Tof1 in stabilizing replication forks at expanded CAG repeats.
• To determine the specific functions of Mrc1 (stabilizer vs. checkpoint activation) in preventing DNA damage and instability at these repeats.

Main Methods:

• Utilized a yeast model system to study replication fork dynamics at medium and long CAG repeat tracts.
• Analyzed the impact of Mrc1 and Tof1 on DNA breakage, cell death, and repeat length instability.

Main Results:

• Mrc1's fork stabilization function, not its checkpoint activation, is critical for preventing DNA breakage and cell death in cells with expanded CAG tracts.
• Both Mrc1 functions are essential for maintaining repeat length stability.
• Tof1's role in preventing fork breakage is specific to long CAG tracts (≥85 repeats).

Conclusions:

• Mrc1 acts as a general fork protector, with its role becoming crucial at longer CAG repeat lengths.
• Long CAG repeats exhibit a specific requirement for Tof1 to maintain fork integrity.
• Fork stabilizers are vital for maintaining replication fork integrity during the replication of structure-forming repeats.