2006. Analysis of a 39-translation enhancer in a tombusvirus: A dynamic model for RNA–RNA interactions of mRNA termini

Tomato bushy stunt virus is a (+)-strand RNA virus that is neither 59-capped nor 39-polyadenylated. Translation of viral proteins is instead mediated by an RNA element, the 39-cap–independent translational enhancer (39CITE), which is located in its 39 untranslated region (UTR). The 39CITE is proposed to recruit the translational machinery to the viral message, while a long-distance RNA–RNA interaction between the 39CITE and 59 UTR is thought to deliver the 43S ribosomal subunit to the 59 end of the viral mRNA. Here we provide the first evidence that the 59 UTR and 39CITE interact physically. Mutational analysis showed that formation of this RNA–RNA interaction in vitro correlates well with efficient translation in vivo, thus supporting its functional relevance. Other analyses of the 39CITE confirmed an overall Y-shaped RNA secondary structure and demonstrated the importance of numerous minor structural features for efficient translation of viral mRNAs. Functional studies on the role of the 59 UTR revealed that despite the absence of a cap structure, 43S subunits load at the very 59 end and scan in a 39 direction. These results indicate that the 59–39 RNA–RNA interaction is likely disrupted by scanning ribosomal subunits and suggest a dynamic model for the interaction of mRNA termini during active translation