The amazing diversity of cap-independent translation elements in the 3'-untranslated regions of plant viral RNAs.

Many plant viral RNAs lack the 5'-cap structure that is required on all host mRNAs for interacting with essential translation initiation factors. Instead, uncapped viral RNAs take over the host translation machinery by harbouring sequences that functionally replace the 5'-cap. Recent reports reveal at least eight different classes of CITE (cap-independent translation element) located in the 3'-UTRs (untranslated regions) of various viruses. We describe how the structure and behaviour of each class of element differs from the other classes, suggesting that they recruit translation factors and, ultimately, the ribosome by diverse mechanisms. These results greatly expand our understanding of ways in which mRNAs can recruit ribosomes, and they provide insight into the regulation of virus gene expression.