Differences in the expression of the hepatitis C virus core+1 open reading frame between a nuclear and a cytoplasmic expression system.
The hepatitis C virus (HCV) genome possesses an open reading frame (ORF) overlapping the core gene at +1 nucleotide (core+1 ORF). Initial in vitro studies suggested that the core+1 ORF is translated by a ribosomal -2/+1 frameshift mechanism during elongation of the viral polyprotein. Recent studies, however, based on transfection of mammalian cells with reporter constructs have shown that translation of the core+1 ORF is mediated from internal core+1 codons. To resolve the apparent discrepancies associated with the mechanism of core+1 translation, we examined the expression of the HCV-1 and HCV-1a (H) core+1 ORF in a cytoplasmic transcription system based on Huh-7/T7 cells that constitutively synthesize the T7 RNA polymerase in comparison to that in Huh-7 cells. We showed that the efficiency of both the -2/+1 and -1/+2 frameshift events operating at the HCV-1 core codons 8-11 is significantly enhanced in the Huh-7/T7 cytoplasmic transcription system and is dependent on the presence of the consecutive adenine (A) residues within core codons 8-11. In contrast, internal translation initiation at core+1 codons 85/87 occurs in both the nuclear and cytoplasmic transcription systems and is not repressed by the ribosomal frameshifting event. Finally, although core+1 codons 85/87 is the most efficient site for internal initiation of core+1 translation, it may not be unique, as additional internal core+1 codon(s) appear to drive translation at low levels.
Vassilaki
Niki
N
Molecular Virology Laboratory, Hellenic Pasteur Institute, 127 Vas. Sofias Avenue, Athens 11521, Greece.
Kalliampakou
Katerina I
KI
Molecular Virology Laboratory, Hellenic Pasteur Institute, 127 Vas. Sofias Avenue, Athens 11521, Greece.
Mavromara
Penelope
P
Molecular Virology Laboratory, Hellenic Pasteur Institute, 127 Vas. Sofias Avenue, Athens 11521, Greece.
D000595:Amino Acid Sequence; D001483:Base Sequence; D006528:Carcinoma, Hepatocellular / Q000821:virology; D002460:Cell Line; D002467:Cell Nucleus / Q000821:virology*; D003062:Codon / Q000235:genetics; D003593:Cytoplasm / Q000821:virology*; D015967:Gene Expression Regulation, Viral; D016174:Hepacivirus / Q000235:genetics*; D006801:Humans; D008113:Liver Neoplasms / Q000821:virology; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D016297:Mutagenesis, Site-Directed; D016366:Open Reading Frames; D010957:Plasmids; D011401:Promoter Regions, Genetic; D014162:Transfection; D014758:Viral Core Proteins / Q000737:chemistry / Q000235:genetics*
D003062:Codon; D014758:Viral Core Proteins