Specific tyrosylation of the bulky tRNA-like structure of brome mosaic virus RNA relies solely on identity nucleotides present in its amino acid-accepting domain

Residues specifying aminoacylation by yeast tyrosyl-tRNA synthetase (TyrRS) of the tRNA-like structure present at the 3 ' -end of brome mosaic virus ( BMV) RNA were determined by the in vitro approach using phage T7 transcript s. They correspond to nucleotides equivalent to base-pair C1-G72 and discri minator base A73 in the amino acid-acceptor branch of the molecule. No func tional equivalents of the tyrosine anticodon residues, shown to be weakly i nvolved in tyrosine identity of canonical tRNA(Tyr), were found in the BMV tRNA-like structure. This indicates a behaviour of this large and intricate molecule reminiscent of that of a minihelix derived from an amino acid-acc eptor branch. Furthermore, iodine footprinting experiments performed on a t yrosylable BMV RNA transcript of 196 nt complexed to yeast TyrRS indicate t hat the amino acid-acceptor branch of the viral RNA is protected against cl eavages as well as a hairpin domain, which is possibly located perpendicula rly to its accepting branch. This domain without the canonical anticodon lo op or the tyrosine anticodon acts as an anchor for TyrRS interaction leadin g to a better efficiency of tyrosylation. (C) 2001 Academic Press.