Abstract
The 3' terminal forty nucleotides of tobraviral RNAs readily fold into a tertiary structure, resembling that of tymo- and tobamoviral RNAs. The latter RNAs possess a tRNA-like structure at their 3' end that is recognized by a number of tRNA-specific enzymes (Rietveld et al. (1984), EMBO J. 3, 2613-2619). Characteristic for their aminoacyl acceptor arm is the presence of a so-called pseudoknot which we now also find in a corresponding position at the 3' terminus of TRV RNA2 (PSG strain). The nucleotide sequences of all tobraviral RNAs analysed so far indicate that they all possess a similar 3' terminal structure. A domain resembling the anticodon arm of canonical tRNA is not readily recognizable. TRV RNA2 can be adenylated with CTP, ATP; tRNA nucleotidyl transferase and ATP. It is unable, however, to accept any of the twenty common amino acids when incubated with ATP and aminoacyl-tRNA synthetases from wheat germ or yeast. We conclude that TRV RNA contains a tRNA-like structure, which, in contrast to the tymo- and tobamoviral tRNA-like structures, cannot be aminoacylated. It is unlikely therefore, that aminoacylation of plant viral RNAs with a tRNA-like structure is a prerequisite for viral RNA replication.