A central role for DNA replication forks in checkpoint activation and response

Area of Science:

• Cellular biology
• Molecular genetics
• DNA repair mechanisms

Background:

• Checkpoint proteins Rad53 and Mec1-Ddc2 are known regulators of cellular responses to DNA damage.
• Understanding the specific contributions of downstream effectors to cell viability is critical for comprehending checkpoint function.

Purpose of the Study:

• To investigate the relative importance of various downstream checkpoint pathways in maintaining cell viability after DNA damage.
• To elucidate the role of DNA replication forks in activating and executing the checkpoint response during S phase.

Main Methods:

• Analysis of cell viability under conditions of DNA damage.
• Examination of the roles of mitosis regulation, gene expression changes, and late origin firing in checkpoint-mediated survival.
• Investigation of Ddc2 recruitment to nuclear foci and Rad53 kinase activation.
• Assessment of the requirement for replication fork assembly in checkpoint activation.

Main Results:

• Checkpoint regulation of mitosis, gene expression, and late origin firing contribute only modestly to cell viability.
• The checkpoint is essential for preventing the irreversible breakdown of stalled replication forks.
• Ddc2 recruitment and Rad53 activation occur specifically during S phase and depend on replication fork assembly.

Conclusions:

• DNA replication forks are critical activators of the S phase checkpoint.
• Replication forks are primary effectors of the checkpoint pathway, essential for preventing their own breakdown.
• The checkpoint's primary role in viability lies in stabilizing stalled replication forks during S phase.