Has a role in the initiation of DNA replication. Required at S-phase checkpoint. Also required for the proper activation of RAD53 in response to DNA damage and replication blocks. Interacts with DPB11. Phosphorylated by CDC28 at the onset of S-phase. This phosphorylation, specifically phosphorylation of Thr-84 promotes interaction with DPB11 leading to DNA replication. Dephosphorylated by CDC14. Present with 656 molecules/cell in log phase SD medium. Belongs to the SLD2 family.