The noncapsid protein expressed from ORF-206 of turnip yellow mosaic virus (TYMV) is autocatalytically processed by a papain-like protease, producing N-terminal 150-kDa and C-terminal 70-kDa proteins. By introducing two methionine residues near the N-terminus of the 70-kDa protein, we have obtained N-terminal amino acid sequence of that protein produced from [35S]methionine-labeled in vitro translations. The introduction of methionine residues was demonstrated to not interfere with viral replication or proteolysis, as assayed by inoculating mutant RNA transcripts onto whole plants and protoplasts, as well as by translating the RNAs in a rabbit reticulocyte lysate. This has allowed us to determine that the TYMV protease cleaves between alanine1259 and threonine1260 of the precursor protein p206, yielding proteins of calculated Mr 140,618 and 66,037, which will be referred to henceforth as p141 and p66, respectively. The sequence context around the cleavage site is LNGA/TP.
The genomic RNA from turnip yellow mosaic virus presents a 3'-end functionally and structurally related to tRNAs. This report summarizes our knowledge about the peculiar structure of the tRNA-like domain and its interaction with tRNA specific proteins, like RNAse P, tRNA nucleotidyl-transferase, aminoacyl-tRNA synthetases, and elongation factors. It discusses also the biological role of this structure in the viral life cycle. A brief survey of our knowledge of other tRNA mimicries in biological systems, as well as their relevance for understanding canonical tRNA, will also be presented.
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