Identification of the cleavage site recognized by the turnip yellow mosaic virus protease

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 [S-35] 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 alanine(1259) and threonine(1250) of the precursor protein p206, yielding proteins of calculated M(r) 140,618 and 66,037, which will be referred to henceforth as p141 and pas, respectively. The sequence context around the cleavage site is LNGA/TP. (C) 1996 Academic Press, Inc.