Role of the RNA2 3′ non-translated region of Blackcurrant reversion nepovirus in translational regulation

The 3′ non-translated regions (NTRs) of mRNAs of eukaryotes and their viruses often contain translational enhancers (TEs). Blackcurrant reversion nepovirus (BRV) has a genome composed of two uncapped polyadenylated RNAs with very long 3′ NTRs, nucleotide sequences of which are very conserved between different BRV isolates. In this work, we studied a role of the RNA2 3′ NTR in translation, using mutagenesis of the firefly luciferase reporter mRNA, in protoplasts of Nicotiana benthamiana. The RNA2 3′ NTR was found to contain a cap-independent TE (3′ CITE), which must base pair with the 5′ NTR to facilitate translation. The BRV 3′ CITE and poly(A) tail provided a major contribution to translational efficiency, with less input from other 3′ NTR parts. The BRV 3′ CITE does not share similarity in nucleotide sequence and secondary structure with other viruses and thus represents a new class of 3′ CITE.