Interpretation of incomplete aminoacylation of yeast tRNA Phe: evidence for a phenylalanyl-tRNA synthetase catalyzed transconformation of tRNA Phe

Abstract

Summary The aminoacylation of tRNAPheyeast exhibits two types of kinetics according to the batches of tRNA used. The kinetics of aminoacylation of several batches are identical to those generally observed for other tRNAs, and the extent of the aminoacylation can be predicted from the characteristics of the aminoacylation and deacylation reactions. With different batches, the kinetics show an additional slow aminoacylation phase which disappears when tRNAPhe has been previously preincubated with yeast phenylalanyl-tRNA synthetase. This phenomenon can be interpreted by the existence, in these batches, of two populations of tRNAPhe, a first one (66 p. cent of the total population) rapidly aminoacylable, while a second one (33 p. cent) not significantly aminoacylable, is probably transconformed into the aminoacylable form by a specific contact with its synthetase. This effect of incubation with phenylalanyl-tRNA synthetase can be reversed by a denaturation-renaturation treatment of tRNA. The same phenomenon can be observed with tRNAPhe, the «Y base of which has been removed by an acidic treatment. Nevertheless, in this case, the ratio between active and inactive populations in the batches exhibiting abnormal kinetics is quite different from that observed in the batches of intact tRNAPhe. The significance of the occurrence of inactive species in some batches of tRNAPhe is discussed.