Srs2 binding to PCNA and its sumoylation contribute to RPA antagonism during the DNA damage response

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• DNA damage checkpoints are crucial for genome stability, halting cell cycle progression upon genotoxin exposure.
• Checkpoint downregulation allows cell cycle resumption after prolonged stress, but its regulation is not fully understood.
• In yeast, Srs2 DNA helicase is known to downregulate the DNA damage checkpoint by removing RPA and Mec1.

Purpose of the Study:

• To investigate the temporal and spatial regulation of Srs2's anti-checkpoint role.
• To elucidate the regulatory mechanisms controlling Srs2 activity in checkpoint downregulation.
• To understand how Srs2 prevents superfluous RPA removal while allowing checkpoint recovery.

Main Methods:

• Genetic analyses of Srs2 regulatory elements (phosphorylation, sumoylation, protein interactions).
• Checkpoint level assessment in yeast cells.
• Examination of Srs2 binding to PCNA and its effect on RPA removal.

Main Results:

• Srs2's RPA countering role is promoted by its binding to PCNA, recruiting it to specific ssDNA regions.
• Srs2 sumoylation, dependent on Srs2-PCNA interaction and Mec1 activity, further enhances RPA antagonism.
• A two-step model for checkpoint downregulation is proposed, involving Srs2 recruitment and sumoylation upon Mec1 hyperactivation.

Conclusions:

• Srs2 activity is spatially and temporally regulated to ensure efficient checkpoint termination.
• PCNA binding and sumoylation are key regulators of Srs2's role in DNA damage checkpoint recovery.
• This regulation minimizes RPA removal at unprotected ssDNA, preserving DNA integrity.