Properties of Isoaccepting tRNALys, tRNAGlu and tRNAGln from rabbit Reticulocytes and liver. Multiplicity, Codon Recognition and Inactivation by Iodine.

The three tRNA species from rabbit liver and reticulocytes, each corresponding to the codons XAA and XAG(X equals A, G, C) were investigated. The elution patterns of the isoaccepting tRNA subspecies after separation by reversedphase chromatography followed by determination of amino acid acceptance have common and differing characteristics. Three subspecies of tRNALys, two of tRNAGlu and three of tRNAGln have been found in reticulocytes, wheras two subspecies of tRNALys, three of tRNAGlu and four of tRNAGln have been determined in rabbit liver. Examination of codon recognition by means of a ribosome binding assay showed that each subspecies binds exclusively in the presence of only one of the two possible triplets; i.e. wobbling was not found. It has been assumed that this high specificity, which is not to be expected according to the "wobble hypothesis", is due to a 2-thiouracil base in the first position of the anticodon. This was supported by oxidation experiments with iodine. Treatment with iodine significantly reduces the aminoacylation capacity of all subspecies that show specific binding with triplets ending in adenosine. We describe and compare for the first time the characteristics of eucaryotic tRNA species which occupy homologous positions in the codon table. Thus it can be seen that all the investigated subspecies have rigorously specific codon recognition in common, wherby "wobbling" can probably be excluded by a principle that is valid for all the investigated species.