Subunit of a replication-pausing checkpoint complex; the replication fork protection complex (Tof1p-Mrc1p-Csm3p) acts at stalled replication forks and is required for rapid replication fork progression, replisome stabilization under stress, mediating DNA replication checkpoint signaling and promoting sister chromatid cohesion after DNA damage, facilitating gap repair of damaged DNA; required for accurate chromosome segregation during meiosis; forms nuclear foci upon DNA replication stress