EFFICIENT AMINOACYLATION OF RESECTED RNA HELICES BY CLASS-II ASPARTYL-TRANSFER-RNA SYNTHETASE DEPENDENT ON A SINGLE NUCLEOTIDE

We show here that small RNA helices which recapitulate part or all of the acceptor stem of yeast aspartate tRNA are efficiently aminoacylate d by cognate class II aspartyl-tRNA synthetase. Aminoacylation is stro ngly dependent on the presence of the single-stranded G73 'discriminat or' identity nucleotide and is essentially: insensitive to the sequenc e of the helical region. Substrates which contain as few as 3 bp fused to G73CCA(OH) are aspartylated. Their charging is insensitive to the sequence of the loop closing the short helical domains. Aminoacylation of the aspartate mini-helix is not stimulated by a hairpin helix mimi cking the anticodon domain and containing the three major anticodon id entity nucleotides. A thermodynamic analysis demonstrates that enzyme interactions with G73 in the resected RNA substrates and in the whole tRNA are the same. Thus, if the resected RNA molecules resemble in som e way the earliest substrates for aminoacylation with aspartate, then the contemporary tRNA(Asp) has quantitatively retained the influence o f the major signal for aminoacylation in these substrates.