A Novel Interaction of Cap-binding Protein Complexes Eukaryotic Initiation Factor (eIF) 4F and eIF(iso)4F with A Region in the 3′-Untranslated Region of Satellite Tobacco Necrosis Virus

Abstract

Satellite tobacco necrosis virus (STNV) RNA is naturally uncapped at its 5′ end and lacks polyadenylation at its 3′ end. Despite lacking these two hallmarks of eukaryotic mRNAs, STNV-1 RNA is translated very efficiently. A ∼130-nucleotide translational enhancer (TED), located 3′ to the termination codon, is necessary for efficient cap-independent translation of STNV-1 RNA. The STNV-1 TED RNA fragment binds to the eukaryotic cap-binding complexes, initiation factor (eIF) 4F and eIF(iso)4F, as measured by nitrocellulose binding and fluorescence titration. STNV-1 TED is a potent inhibitor of in vitro translation when added in trans. This inhibition is reversed by the addition of eIF4F or eIF(iso)4F, and the subunits of eIF4F and eIF(iso)4F cross-link to STNV-1 TED, providing additional evidence that these factors interact directly with STNV-1 TED. Deletion mutagenesis of the STNV-1 TED indicates that a minimal region of ∼100 nucleotides is necessary to promote cap-independent translation primarily through interaction with the cap binding subunits (eIF4E or eIF(iso)4E) of eIF4F or eIF(iso)4F.