Nucleolin stimulates viral internal ribosome entry site-mediated translation

Previous results from our laboratory have identified a small (60 nt) RNA fr om the yeast S. cerevisiae that specifically inhibits internal ribosome ent ry site (IRES)-mediated translation programmed by poliovirus (PV) and hepat itis C virus (HCV) 5'-untranslated region (5'UTR). The yeast inhibitor RNA (called IRNA) was found to efficiently compete with viral 5'UTR for binding of several cellular polypeptides that presumably play important roles in I RES-mediated translation. One such IRNA (and 5'UTR)-binding protein has pre viously been identified as the La autoantigen. In this report, we have iden tified a 110-kDa IRNA-binding protein (which also interacts with viral 5'UT R) as nucleolin, a nucleolar RNA binding protein that was previously shown to translocate into the cytoplasm following infection of cells with poliovi rus. We demonstrate that nucleolin (called C23) stimulates viral IRES-media ted translation both in vitro and in vivo. We also show that nucleolin muta nts containing the carboxy-terminal RNA binding domains but lacking the ami no terminal domain inhibit IRES-mediated translation in vitro. The translat ion inhibitory activity of these mutants correlates with their ability to b ind the 5'UTR sequence. These results suggest a role of nucleolin/C23 in vi ral IRES-mediated translation. (C) 2001 Elsevier Science B.V. All rights re served.