ATR and infection: For example, porcine circovirus type 2 (PCV2) promotes its replication by inducing host cells into the S phase, swine fever virus (CSFV) increases the expression of P53 to arrest the cell cycle in G1 during infection, and simian virus 40 (SV40) activates ATR-Delta P53 signaling, maintaining the host in the S phase to create an optimal environment for SV40 replication [34–36].