ISG15 and infection: However, compared to the WT virus, infection with the K272R mutant virus resulted in significantly lower expression of interferon-stimulated genes (ISGs), including interferon-induced protein with tetratricopeptide repeats 1 (IFIT1), interferon stimulated gene 15 (ISG15), and Myxovirus resistance protein A (MxA) (Fig. 5D–F), in a dose-dependent manner (Fig. S1).