Mrc1/Claspin: a new role for regulation of origin firing.

Mrc1 and its vertebrate homologue Claspin serve as a mediator for replication stress checkpoint signaling, receiving the signal from Mec1/Rad3/ATR sensor kinase and transmitting it to the effector Rad53/Cds1/Chk1 kinase. They are likely to be a part of the replisome and facilitate the S-phase progression by promoting replication fork progression. Recent reports on Mrc1/Claspin indicate their new role in regulating the replication initiation through interaction with Cdc7, a key conserved serine-threonine kinase that triggers firing at each replication origin. Mrc1/Claspin has a specific domain that specifically interacts with Cdc7, and this domain is involved also in intramolecular interaction with its N-terminal segment. Mechanisms for novel regulation of origin firing and its timing through recruitment of Cdc7 to Mrc1/Claspin will be discussed.