Involvement of transfer ribonucleic acid in early reactions of polyphenylalanine synthesis

Abstract

The involvement of transfer RNA in the reactions associated with the initiation of polypeptides on ribosomes has been studied in a polyuridylic acid-directed transfer system derived from rabbit reticulocytes. It is shown that activity for these initial reactions is proportional to phenylalanine acceptance capacity in preparations of deacylated transfer RNA, and that near maximum activity is obtained at a ratio of less than 0.25 molecule of transfer RNA of the phenylalanine acceptor type per ribosome. This may reflect a specific, codon-directed interaction of deacylated transfer RNA with active ribosomes capable of synthesizing polyphenylanine. The activity of deacylated transfer RNA in these early reactions of protein synthesis shows an absolute dependence for the 3′ terminal adenosine moiety. Removal of the 3′ terminal adenosine produces transfer RNA molecules which are capable of inhibiting the initial reactions of protein synthesis. The possible significance of these reactions for the regulation of protein synthesis is discussed.