A translational enhancer derived from tobacco mosaic virus is functionally equivalent to a Shine-Dalgarno sequence

When present at the 5′ end of mRNAs, the untranslated leader sequence (Ω ) of tobacco mosaic virus RNA significantly enhances translation in eukaryotes and prokaryotes. We have tested a deletion derivative of the Ω sequence, Ω Δ 3, for its enhancing ability on gene constructs in which the ribosomal binding site was either present or deleted, in several Gram-negative bacterial species including Escherichia coli, Agrobacterium tumefaciens, Xanthomonas campestris pv. vitians, Erwinia amylovora, and Salmonella typhimurium. In vivo production of chloramphenicol acetyltransferase from a gene construct lacking its native ribosomal binding site was enhanced 40- to 120-fold by the presence of Ω Δ 3. Similar levels of enhancement (30- to 240-fold) were observed when the gene encoding β -glucuronidase was tested. With a chloramphenicol acetyltransferase construct containing a ribosomal binding site, enhancement was markedly less, between 1- and 3.8-fold. Ω Δ 3 appeared to enhance translation independent of its position upstream of the AUG codon used for initiation.