The 5' and 3' untranslated regions of satellite tobacco necrosis virus RNA affect translational efficiency and dependence on a 5' cap structure.

Satellite tobacco necrosis virus RNA (STNV RNA) is a naturally uncapped viral RNA that contains 1239 nucleotides: 29 in the 5' untranslated region (UTR), 591 in the coding region and 619 in the 3' UTR. Mutations were made in the 5' and 3' UTRs, and the effects of these mutations on translational efficiency and cap independence were measured in an in vitro translation system from wheat germ. Removal of the first 12 nucleotides or 10 changes in the nucleotide sequence of the 5' UTR reduced translational efficiency approximately 3-fold; capping of these 5' mutant mRNAs restored their translational efficiencies. Truncation of the 3' UTR to nucleotide 627 or 700, or deletion of nucleotides 627-737, reduced translational efficiency more than 20-fold; capping of these 3' mutant mRNAs restored their translational efficiencies. These modifications in the 3' UTR increased the concentration of initiation factor 4F required for translation. Chimeric mRNAs were constructed which contained the coding region of rabbit alpha-globin mRNA and either the 5' UTR, 3' UTR, or both the 5' and 3' UTRs of STNV RNA. Both the 5' and 3' UTRs of STNV RNA were necessary to obtain cap-independent translation. These findings indicate that interaction between 5' UTR and the region between nucleotides 627 and 737 in the 3' UTR are required for cap-independent translation.