The observation that poliovirus mRNA is not translated in the yeast Saccharomyces cerevisiae has led to the discovery of a small RNA (60 nt, called IRNA, inhibitor RNA) which was later shown to specifically inhibit internal ribosome entry site (IRES)-mediated translation of naturally uncapped mRNAs. Translation of cellular capped mRNAs was not significantly inhibited by IRNA. IRNA also specifically inhibited hepatitis C virus (HCV) IRES-mediated translation in vitro and in vivo. A hepatoma cell line constitutively expressing IRNA was refractory to infection by a chimeric poliovirus (PV/HCV) in which PV IRES is replaced by HCV-IRES. In contrast, a PV/EMCV chimeric virus containing the EMCV IRES was not significantly inhibited in the IRNA-hepatoma cell line compared to the control hepatoma cells. UV-crosslinking studies showed that the IRNA binds a number of cellular proteins that appear to be important for IRES-mediated translation. Interaction of these proteins with the viral IRES elements is believed to be important in recruiting ribosomes to the 5´ UTR of viral RNAs. The binding of the purified La autoantigen to the HCV IRES element was efficiently and specifically competed by IRNA. These results provide a basis for development of novel drugs effective against HCV infection.