LOCAL AND DISTANT SEQUENCES ARE REQUIRED FOR EFFICIENT READTHROUGH OFTHE BARLEY YELLOW DWARF VIRUS PAV COAT PROTEIN GENE STOP CODON

Many viruses use stop codon readthrough as a strategy to produce exten ded coat or replicase proteins. The stop codon of the barley yellow dw arf virus (PAV serotype) coat protein gene is read through at a low ra te. This produces an extended polypeptide which becomes part of the vi rion. We have analyzed the cis-acting sequences in the barley yellow d warf virus PAV genome required for this programmed readthrough in vitr o in wheat germ extracts and reticulocyte lysates and in vivo in oat p rotoplasts. Two regions 3' to the stop codon were required. Deletion o f sections containing the first 5 of the 16 CCN NNN repeats located 3' of the stop codon greatly reduced readthrough in vitro and in vivo. S urprisingly, readthrough also required a second, more distal element t hat is located 697 to 758 bases 3' of the stop codon within the readth rough open reading frame. This element also functioned in vivo in oat protoplasts when placed more than 2 kb from the coat protein gene stop in the untranslated region following a GUS reporter gene. This is the first report of a long-range readthrough signal in viruses.