G1/S host cell cycle checkpoint dysregulation by virus

Upon infection, viruses alter the environment of infected cells in order to replicate more efficiently. Modulation of host cell cycle progression is commonly used to maximize viral replication. Among the key steps, transition from the G1 to S phase is deregulated by many viral proteins. Members of the retinoblastoma (Rb) family of tumors repressors are transcriptional regulators that critically regulate the G1 phase.

Many viruses deregulate G1/S transition of the host cell cycle either to inhibit or to activate the transition.