Detalle de: Analysis of the interacting partners eIF4F and 3′‐CITE required for Melon necrotic spot virus cap‐independent translation

Summary We have shown previously that the translation of Melon necrotic spot virus (MNSV, family Tombusviridae , genus C armovirus ) RNAs is controlled by a 3′‐cap‐independent translation enhancer (CITE), which is genetically and functionally dependent on the eukaryotic translation initiation factor (eIF) 4E. Here, we describe structural and functional analyses of the MNSV‐Mα5 3′‐CITE and its translation initiation factor partner. We first mapped the minimal 3′‐CITE (Ma5TE) to a 45‐nucleotide sequence, which consists of a stem‐loop structure with two internal loops, similar to other I‐shaped 3′‐CITEs. UV crosslinking, followed by gel retardation assays, indicated that Ma5TE interacts in vitro with the complex formed by eIF4E + eIF4G 980–1159 (eIF4F p20 ), but not with each subunit alone or with eIF4E + eIF4G 1003–1092 , suggesting binding either through interaction with eIF4E following a conformational change induced by its binding to eIF4G 980–1159 , or through a double interaction with eIF4E and eIF4G 980–1159 . Critical residues for this interaction reside in an internal bulge of Ma5TE, so that their mutation abolished binding to eIF4E + eIF4G 1003–1092 and cap‐independent translation. We also developed an in vivo system to test the effect of mutations in eIF4E in Ma5TE‐driven cap‐independent translation, showing that conserved amino acids in a positively charged RNA‐binding motif around amino acid position 228, implicated in eIF4E–eIF4G binding or belonging to the cap‐recognition pocket, are essential for cap‐independent translation controlled by Ma5TE, and thus for the multiplication of MNSV.