The 5' untranslated region of Perina nuda virus (PnV) possesses a strong internal translation activity in baculovirus-infected insect cells

A bicistronic baculovirus expression vector and fluorescent protein-based assays were used to identify the sequences that possess internal translation activity in baculovirus-infected insect cells. We demonstrated that the 5' untranslated region (5'UTR; 473 nucleotides) of Perina nuda virus (PnV) and the 5'UTR (579 nucleotides) of Rhopalosiphum padi virus (RhPV), but not the IRES sequence of Cricket paralysis virus, have internal translation activity in baculovirus-infected Sf21 cells. In addition, we found that including the first 22 codons of the predicted PnV open reading frame (ORF; a total of 539 nucleotides) enhanced internal translation activity by approximately 18 times. This is the first report of internal translation activity for a baculovirus expression system (BEVS) in the iflavirus 5' sequence and may facilitate the development of polycistronic baculovirus transfer vectors that can be used in BEVS for the production of multiple protein complexes.