Figure 8.

 Model for the function of Cds1 in the S-phase arrest response. (A) Checkpoint Rad-dependent activation of Cds1 by perturbations to S-phase acts to ensure both S-phase arrest, by phosphorylating components of the replication complex, and mitotic arrest by phosphorylating a substrate that leads to inactivation of the mitotic apparatus. (B) Cds1 only acts to phosphorylate and stabilize the replication machinery. This prevents inappropriate DNA damage and maintains the structure(s) that are activating a Cds1 independent mitotic arrest signal. This signal would also be independent of the checkpoint Rad proteins, until such time as replication was perturbed, when maintenance of the appropriate replication structures becomes a prerequisite.