AMINOACYLATION IDENTITY SWITCH OF TURNIP YELLOW MOSAIC-VIRUS RNA FROMVALINE TO METHIONINE RESULTS IN AN INFECTIOUS VIRUS

The turnip yellow mosaic virus genomic RNA terminates at its 3' end in a tRNA-like structure that is capable of specific valylation, By dire cted mutation, the aminoacylation specificity has been switched from v aline to methionine, a novel specificity for viral tRNA-like structure s, The switch to methionine specificity, assayed in vitro under physio logical buffer conditions with wheat germ methionyl-tRNA synthetase, r equired mutation of the anticodon loop and the acceptor stem pseudokno t. The resultant methionylatable genomes are infectious and stable in plants, but genomes that lack strong methionine acceptance (as previou sly shown with regard to valine acceptance) replicate poorly, The resu lts indicate that amplification of turnip yellow mosaic virus RNA requ ires aminoacylation, but that neither the natural (valine) specificity nor interaction specifically with valyl-tRNA synthetase is crucial.