DNA replication and DNA repair are essential cell cycle steps ensuring correct transmission of the genome. The feedback replication control system links mitosis to completion of DNA replication and partially overlaps the radiation checkpoint control. Deletion of the chk1/rad27 gene abolishes the radiation but not the replication feedback control. Thermosensitive mutations in the DNA polymerase delta, cdc18 or cdc20 genes lead cells to arrest in the S phase of the cell cycle. We show that strains carrying any of these mutations enter lethal mitosis in the absence of the radiation checkpoint chk1/rad27. We interpret these data as an indication that an assembled replisome is essential for replication dependent control of mitosis and we propose that the arrest of the cell cycle in the thermosensitive mutants is due to the chk1+/rad27+ pathway, which monitors directly DNA for signs of damage.