E2F1 and infection: Although DNA viruses promote cell cycle progression and prevent apoptosis, RNA viruses for example HIV, coronavirus IBV, and influenza virus arrest cell cycle at an early stage of infection.50, 51, 52 These reports, together with role of API5 in cell proliferation, raise a compelling possibility that regulation of API5 by NP in IAV-infected cells, apart from its role in apoptosis, may also impact E2F1-mediated cell cycle control.