Binding of Glycyl-tRNA synthetase to Mengovirus RNA stimulates translation

Picornaviruses are small viruses with a plus-strand RNA genome in which RNA secondary structures bind cellular proteins to support viral translation and replication. Here, we characterize tRNA anticodon stem-loop-like structures in the 5'- and 3' untranslated regions (UTRs) of the RNA of Mengovirus, a member of the Cardiovirus group in the Picornaviridae family. These RNA elements specifically bind cellular Glycyl-tRNA synthetase (GARS). Mutation of the conserved CCA motifs in the loops of these GARS binding elements (GBEs) impairs binding, as does deletion of the anticodon binding domain of GARS. Mutation of the 3'-UTR GBE reduces Mengovirus translation early after transfection, independent of viral polymerase activity. The 3'UTR GBE is a stronger GARS binding site, and in reporter RNAs with the Mengovirus 5'- and 3'-UTRs, the 3'UTR GBE strongly contributes to recruitment of translation factors and ribosomes, thereby stimulating translation. In contrast, the 5'UTR GBE is a weaker GARS binding site, but its mutation has a stronger effect on translation. Therefore, we hypothesize that a GARS dimer binds strongly to an "anchor" site in the 3'UTR with one monomer, while the other monomer interacts with the 5'UTR to stimulate recruitment of translation factors and ribosomes.