Protein expression strategies in Tobacco necrosis virus-D

Tobacco necrosis virus (TNV-D) has a plus-strand RNA genome that is neither 5′ capped nor 3′ poly-adenylated. Instead, it utilizes a 3′ cap-independent translational enhancer (3′CITE) located in its 3′ untranslated region (UTR) for translation of its proteins. We have examined the protein expression strategies used by TNV-D and our results indicate that: (i) a base pairing interaction between conserved ACCA and UGGU motifs in the genomic 5′UTR and 3′CITE, respectively, is not required for efficient plant cell infection, (ii) similar potential 5′UTR-3′CITE interactions in the two viral subgenomic mRNAs are not needed for efficient translation of viral proteins in vitro, (iii) a small amount of capsid protein is translated from the viral genome by a largely 3′CITE-independent mechanism, (iv) the larger of two possible forms of capsid protein is efficiently translated, and (v) p7b is translated from subgenomic mRNA1 by a leaky scanning mechanism.