The turnip yellow mosaic virus tRNA-like structure cannot be replaced by generic tRNA-like elements or by heterologous 3' untranslated regions known to enhance mRNA expression and stability.

The tRNA-like structure (TLS) at the 3' end of the turnip yellow mosaic virus genome was replaced with heterologous tRNA-like elements, and with a poly(A) tail, in order to assess its role. Replacement with the valylatable TLSs from two closely related tymoviruses resulted in infectious viruses. In contrast, no systemic symptoms on plants, and only low viral accumulations in protoplasts, were observed for three chimeric genomes with 3' sequences known to enhance mRNA stability and translatability. One of these chimeras had a poly(A) tail, and the others had the TLS with associated upstream pseudoknot tracts from the 3' ends of brome mosaic and tobacco mosaic viruses. The latter two chimeric RNAs were shown to be appropriately folded by demonstrating their aminoacylation in vitro with tyrosine and histidine, respectively. The results show that enhancement of genome stability or gene expression is not the major role of the turnip yellow mosaic virus TLS. The major role is likely to be replicational, dependent on features present in tymoviral TLSs but not in generic tRNA-like structures.