Aminoacyl-transfer RNA synthetase recognition code-words in yeast transfer RNA's: A proposal

Abstract

A hypothesis explaining the observed specificity in respect of the recognition of specific transfer RNA's ‡ by aminoacyl-tRNA synthetases is presented. Available evidence, although not decisive, seems to favour the view that the synthetase recognizes a specific nucleotide sequence (“synthetase recognition code-word”) in the tRNA. If this is true, it is argued that the amino acids should bear the same relationship to each other in respect of their synthetase recognition code-words as they do in respect of their codons. The nucleotide sequences of five yeast tRNA's are analysed in the light of the above premise, and a possible set of synthetase recognition code-words for all the amino acids in yeast, excepting methionine, is proposed. The suggested three letter synthetase recognition code-words begin with either adenine or uracil, and in the case of the five yeast tRNAs of known structure, occur in the same region of the RNA molecule; they may be recognized by the appropriate yeast synthetase only if certain constraints, which are stated, are satisfied. Available evidence supporting the proposed assignments is summarized, and some predictions made. It would seem that the synthetase recognition code—in a way the second genetic code—is species specific.