Properties of Isoaccepting Species of Lysine tRNA from Rabbit Reticulocytes in Codon Recognition and in Haemoglobin Biosynthesis <i>in vitro</i>

Abstract

Four isoaccepting species of tRNA Lys from rabbit‐reticulocyte lysate were separated by reversed‐phase chromatography–2. The binding of species II and III to Escherichia coli ribosomes is stimulated by the trinucleotide AAG, whereas binding of the same species stimulated by AAA is not observed. tRNA Lys IV , on the other hand, responds preferentially to the codon AAA. A completely homologous system has been used for the insertion of lysine into the haemoglobin polypeptide chains. Compared to the insertion of lysine by unseparated species of tRNA Lys , the species II and III incorporated lysine predominantly into the α‐chain, whereas lysine from Lys‐tRNA Lys IV was transferred preferentially into the β‐chain. From this the conclusion can be drawn, that the codon specificities of the three species of tRNA Lys from reticulocytes are not completely in line with the wobble hypothesis proposed by Crick. All species respond almost exclusively only to one of the two triplets specific for lysine. In haemoglobin‐mRNA translation the isoaccepting tRNA Lys species have a more differentiated function. Therefore, the multiplicity of tRNA species is not a phenomenon of mere redundancy.