title: Lower concentration of La protein required for internal ribosome entry on hepatitis C virus RNA than on poliovirus RNA.
abstract: Translation initiation of poliovirus and hepatitis C virus (HCV) RNA occurs by entry of ribosomes to the internal RNA sequence, called the internal ribosomal entry site (IRES). Both IRES bind to the La protein and are thought to require the protein for their translation initiation activity, although they are greatly different in both the primary and predicted secondary structures. To compare the La protein requirement for these IRES, we took advantage of I-RNA from the yeast Saccharomyces cerevisiae, which has been reported to bind to La protein and block poliovirus IRES-mediated translation initiation. In a cell-free translation system prepared from HeLa cells, yeast I-RNA inhibited translation initiation on poliovirus RNA as expected, but did not significantly inhibit translation initiation on HCV RNA. However, the translation initiation directed by either IRES was apparently inhibited by I-RNA in rabbit reticulocyte lysates, in which La protein is limiting. I-RNA-mediated inhibition of HCV IRES-dependent translation in rabbit reticulocyte lysates was reversed by exogenous addition of purified recombinant La protein of smaller amounts than necessary to reverse poliovirus IRES-dependent translation. These results suggest that HCV IRES requires lower concentrations of La protein for its function than does poliovirus IRES. Immunofluorescence studies showed that HCV infection appeared not to affect the subcellular localization of La protein, which exists mainly in the nucleus, although La protein redistributed to the cytoplasm after poliovirus infection. The data are compatible with the low requirement of La protein for HCV IRES activity.
authors.affiliation: Department of Microbiology, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan1.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Isoyama
authors.affiliation: Department of Microbiology, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan1.
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Kamoshita
authors.affiliation: Department of Microbiology and Immunology, Tokyo Metropolitan Institute for Neuroscience, 2-6 Musashidai, Fuchu-shi, Tokyo 183-8526, Japan2.
authors.forename: Kotaro
authors.initials: K
authors.lastname: Yasui
authors.affiliation: Department of Microbiology, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan1.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Iwai
authors.affiliation: Department of Microbiology, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan1.
authors.forename: Kazuko
authors.initials: K
authors.lastname: Shiroki
authors.affiliation: Department of Microbiology, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan1.
authors.forename: Haruka
authors.initials: H
authors.lastname: Toyoda
authors.affiliation: Department of Internal Medicine, Sagamihara National Hospital, 18-1 Sakuradai, Sagamihara, Kanagawa 228-0815, Japan3.
authors.forename: Akio
authors.initials: A
authors.lastname: Yamada
authors.affiliation: Division of Rheumatology, Department of Medicine, Juntendo University, School of Medicine, 3-1-3 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan4.
authors.forename: Yoshinari
authors.initials: Y
authors.lastname: Takasaki
authors.affiliation: Department of Microbiology, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan1.
authors.forename: Akio
authors.initials: A
authors.lastname: Nomoto
mesh_terms: D000818:Animals; D001324:Autoantigens / Q000502:physiology*; D006367:HeLa Cells; D016174:Hepacivirus / Q000235:genetics*; D006801:Humans; D017955:Poliovirus / Q000235:genetics*; D014176:Protein Biosynthesis; D012367:RNA, Viral / Q000378:metabolism*; D011817:Rabbits; D012261:Ribonucleoproteins / Q000502:physiology*; D012270:Ribosomes / Q000378:metabolism*; D000097585:SS-B Antigen
chemical_list: D001324:Autoantigens; D012367:RNA, Viral; D012261:Ribonucleoproteins; D000097585:SS-B Antigen