The 3'-untranslated region (UTR) of tobacco mosaic virus (TMV), which terminates in a tRNA-like structure, functionally substitutes for a poly(A) tail in both plant and animal cells. The addition of the TMV 3'-UTR to chimeric mRNA constructs increases their expression up to 100-fold, increasing both translational efficiency and mRNA stability. The domain largely responsible for the regulation maps to a 72 base region immediately upstream of the tRNA-like structure, however, the 3'-terminal, tRNA-like structure is required for full function. Its contribution is lost if separated from the upstream pseudoknot domain by as few as 5 bases or if 6 bases are removed from the 3'-terminus. Sequence addition to the 3'-terminus of the TMV 3'UTR or the upstream pseudoknot domain inhibits function in both tobacco and Chinese hamster ovary cells.