IFIT1 and infection: Knocking down IFIT1, IFIT2, and IFIT3 in HeLa cells with siRNA resulted in an increase rate of infection by viruses known to display a PPP-RNA nucleic acid species during their life cycle such as Rift Valley fever virus (RVFV), vesicular stomatitis virus (VSV), and influenza A. In contrast, growth of Encephalomyocarditis virus (EMCV), which does not produce a PPP-RNA species, was unaffected by the presence or absence of IFIT1 (13).