OPERATIONAL RNA CODE FOR AMINO-ACIDS - SPECIES-SPECIFIC AMINOACYLATION OF MINIHELICES SWITCHED BY A SINGLE NUCLEOTIDE

The genetic code is based on aminoacylation reactions where specific a mino acids are attached to tRNAs bearing anticodon trinucleotides. How ever, the anticodon-independent specific aminoacylation of RNA minihel ix substrates by bacterial and yeast tRNA synthetases suggested an ope rational RNA code for amino acids whereby specific RNA sequences/struc tures in tRNA acceptor stems correspond to specific amino acids, Becau se of the possible significance of the operational RNA code for the de velopment of the genetic code, we investigated aminoacylation of synth etic RNA mini-helices with a human enzyme to understand the sequences needed for that aminoacylation compared with those needed for a microb ial system. We show here that the species-specific aminoacylation of g lycine tRNAs is recapitulated by a species-specific aminoacylation of minihelices. Although the mammalian and Escherichia coli minihelices d iffer at 6 of 12 base pairs, two of the three nucleotides essential fo r aminoacylation by the E. coli enzyme are conserved in the mammalian minihelix. The two conserved nucleotides were shown to be also importa nt for aminoacylation of the mammalian minihelix by the human enzyme. A simple interchange of the differing nucleotide enabled the human enz yme to now charge the bacterial substrate and not the mammalian minihe lix. Conversely, this interchange made the bacterial enzyme specific f or the mammalian substrate, Thus, the positional locations (if not the actual nucleotides) for the operational RNA code for glycine appear c onserved from bacteria to mammals.