A single-stranded loop in the 5 ' untranslated region of cucumber mosaic virus RNA 4 contributes to competitive translational activity

The 5' untranslated region (UTR) of cucumber mosaic virus (CMV) RNA 4 confe rs a highly competitive translational advantage on a heterologous luciferas e open reading frame. Here we investigated whether secondary structure in t he 5' UTR contributes to this translational advantage. Stabilization of the 5' UTR RNA secondary structure inhibited competitive translational activit y. Alteration of a potential single-stranded loop to a stem by substitution mutations greatly inhibited the competitive translational activity. Tobacc o plants infected with wild type virus showed a 2.5-fold higher accumulatio n of maximal coat protein than did plants infected with a loop-mutant virus . Amplification of viral RNA in these plants could not explain the differen ce in accumulation of coat protein. Phylogenetic comparison showed that pot ential single-stranded loops of 12-23 nucleotides in length exist widely in subgroups of CMV. (C) 1999 Federation of European Biochemical Societies.