Hepatitis C virus internal ribosome entry site (IRES) stem loop IIId contains a phylogenetically conserved GGG triplet essential for translation and IRES folding

J Virol. 2000 Nov;74(22):10430-7. doi: 10.1128/jvi.74.22.10430-10437.2000.


The hepatitis C virus (HCV) internal ribosome entry site (IRES) is a highly structured RNA element that directs cap-independent translation of the viral polyprotein. Morpholino antisense oligonucleotides directed towards stem loop IIId drastically reduced HCV IRES activity. Mutagenesis studies of this region showed that the GGG triplet (nucleotides 266 through 268) of the hexanucleotide apical loop of stem loop IIId is essential for IRES activity both in vitro and in vivo. Sequence comparison showed that apical loop nucleotides (UUGGGU) were absolutely conserved across HCV genotypes and the GGG triplet was strongly conserved among related Flavivirus and Pestivirus nontranslated regions. Chimeric IRES elements with IIId derived from GB virus B (GBV-B) in the context of the HCV IRES possess translational activity. Mutations within the IIId stem loop that abolish IRES activity also affect the RNA structure in RNase T(1)-probing studies, demonstrating the importance of correct RNA folding to IRES function.

MeSH terms

  • 5' Untranslated Regions
  • Base Sequence
  • Cell Line
  • Conserved Sequence
  • Hepacivirus / genetics
  • Hepacivirus / metabolism*
  • Molecular Sequence Data
  • Nucleic Acid Conformation
  • Oligonucleotides, Antisense / metabolism
  • Phylogeny
  • Point Mutation
  • Protein Biosynthesis*
  • RNA, Untranslated / chemistry
  • RNA, Untranslated / genetics
  • RNA, Viral / chemistry*
  • RNA, Viral / genetics*
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Ribonucleases / metabolism
  • Ribosomes / metabolism*
  • Transcription, Genetic
  • Trinucleotide Repeats / genetics


  • 5' Untranslated Regions
  • Oligonucleotides, Antisense
  • RNA, Untranslated
  • RNA, Viral
  • Recombinant Fusion Proteins
  • Ribonucleases