Lower concentration of La protein required for internal ribosome entry on hepatitis C virus RNA than on poliovirus RNA.
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.
Isoyama
Takeshi
T
Department of Microbiology, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan1.
Kamoshita
Nobuhiko
N
Department of Microbiology, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan1.
Yasui
Kotaro
K
Department of Microbiology and Immunology, Tokyo Metropolitan Institute for Neuroscience, 2-6 Musashidai, Fuchu-shi, Tokyo 183-8526, Japan2.
Iwai
Atsushi
A
Department of Microbiology, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan1.
Shiroki
Kazuko
K
Department of Microbiology, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan1.
Toyoda
Haruka
H
Department of Microbiology, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan1.
Yamada
Akio
A
Department of Internal Medicine, Sagamihara National Hospital, 18-1 Sakuradai, Sagamihara, Kanagawa 228-0815, Japan3.
Takasaki
Yoshinari
Y
Division of Rheumatology, Department of Medicine, Juntendo University, School of Medicine, 3-1-3 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan4.
Nomoto
Akio
A
Department of Microbiology, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan1.
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
D001324:Autoantigens; D012367:RNA, Viral; D012261:Ribonucleoproteins; D000097585:SS-B Antigen