A sequence located 4.5 to 5 kilobases from the 5′ end of the barley yellow dwarf virus (PAV) genome strongly stimulates translation of uncapped mRNA

Abstract

An infectious, in vitro transcript from a full-length cDNA clone of the barley yellow dwarf virus (PAV serotype) genome translated efficiently in a wheat germ translation extract. Deletions in a region that we call the 3′ translational enhancer, located between bases 4,513 and 5,009 in the 5,677-base genome, reduced translation of the 5′-proximal open reading frames from uncapped RNA by at least 30-fold. Deletions elsewhere in all but the 5′ end of the genome had no effect on translation. Presence of a m7G(5′)ppp(5′)G cap on the 5′ end fully restored translational efficiency of transcripts lacking the 3′ translational enhancer. The translation enhancer reduced inhibition of translation by free cap analog, did not affect RNA stability, and did not function in reticulocyte lysates. When placed in the 3′-untranslated region of uncapped mRNA encoding the β-glucuronidase gene, the translation enhancer stimulated translation more than 80-fold, in the presence of the viral, but not a plasmid-derived, 5′ leader. A polyadenylate tail could not substitute for the 3′ translation enhancer. These observations provide an extreme example, in terms of distance from the 5′ end and level of stimulation, of an mRNA in which a sequence near the 3′ end stimulates translation.