It still remains possible that multiple pathways, which can be checkpoint-dependent or -independent and act in a cell-cycle-regulated manner, are involved in damage-induced Cdt1 degradation. Damage-induced Cdt1 degradation may also contribute to the prevention of DNA re-replication. Upon DNA damage, checkpoints are activated and consequently Cdk activities are reduced so that cell cycle is arrested, meanwhile reduced Cdk activity in G2 may allow reassembly of pre-RCs on already fired origins