The 5'-untranslated leader sequence of potato virus X RNA enhances the expression of a heterologous gene in vivo.

The 5' untranslated leader of potato virus X (PVX) RNA is shown when contiguous to the coding sequence, to enhance the expression of the neomycin phosphotransferase II gene (NPTII) in Nicotiana tabacum protoplasts in vivo. The level of transient expression of the NPTII gene in protoplasts provided by a plasmid containing the coding sequence of the NPTII gene under the control of 35S cauliflower mosaic virus (CaMV) promoter and terminator elements served as the baseline control. Insertion of the viral 5' untranslated leader sequence upstream of the NPTII ATG codon increased the level of expression 4-fold. An 83 nucleotide (nt) leader sequence (lacking only one nucleotide of the complete PVX leader) and a truncated version with a 28 deletion at the 3' end both had similar enhancing abilities. The 28 nt CA region of the PVX leader alone had no enhancement properties.