Subunit of a replication-pausing checkpoint complex; the replication fork protection complex (Tof1p-Mrc1p-Csm3p) acts at stalled forks and is required for rapid replication fork progression, replisome stabilization under stress, mediating checkpoint signaling and promoting sister chromatid cohesion after damage, facilitating gap repair of damaged DNA; interacts with the MCM helicase; recruits Top1p to the fork to suppress DNA damage; relocalizes to the cytosol in response to hypoxia to hypoxia