Roles of Rad18 and Polκ in tolerance of CDK2-induced DNA replication stress. MK-1775 treatment de-represses CDK2 and CDK1 activities, which induce DNA replication stress and aberrant G2/M progression, respectively. Rad18 and Polκ prevent accumulation of post-replicative ssDNA gaps arising from aberrant CDK2 activity. In the absence of Rad18 or Polκ, CDK2-induced ssDNA persists into mitosis (because of aberrant CDK1 activity) and triggers PCC.