Mrc1 and Rad9 cooperate to regulate initiation and elongation of DNA replication in response to DNA damage

Area of Science:

• Cellular biology
• Molecular genetics
• DNA replication

Background:

• The S-phase checkpoint is crucial for maintaining genome integrity during DNA replication stress.
• In budding yeast, Mec1 initiates this pathway, amplified by Rad53 activation through mediators Mrc1 and Rad9.
• Mrc1 promotes Rad53 activation at stalled forks, while Rad9 is a general DNA damage response mediator.

Purpose of the Study:

• To investigate the interplay between Mrc1 and Rad9 in response to DNA damage.
• To elucidate their distinct but complementary mechanisms in controlling DNA replication.

Main Methods:

• Investigated the roles of Mrc1 and Rad9 in budding yeast.
• Analyzed checkpoint signaling and DNA replication control under stress conditions.

Main Results:

• Mrc1 rapidly activates Rad53 at stalled forks and represses late-firing origins, but this repression is transient.
• Rad9 subsequently takes over to maintain continuous checkpoint signaling.
• Rad9-mediated Rad53 activation slows down DNA replication fork progression.

Conclusions:

• Mrc1 and Rad9 have distinct functions in the S-phase checkpoint.
• These mediators work complementarily to ensure optimal S-phase completion under replication stress.
• The S-phase checkpoint regulates both initiation and elongation of DNA replication during damage response.