Aminoacyl derivatives of nucleosides, nucleotides, and polynucleotides. 23. Enzymic binding of aminoacyl transfer ribonucleic acid to ribosomes: the study of binding sites of 2' and 3' isomers of aminoacyl transfer ribonucleic acid

Abstract

The mechanism of enzymatic binding of AA[aminoacyl]-tRNA to the acceptor site of Escherichia coli ribosomes was studied using the following aminoacyl oligonucleotides as models of the 3'' terminus of AA-tRNA: C-A-Phe, C-A-(2''-Phe)H, and C-2(2''H)Phe. T-.psi.-C-Gp was used as a model of loop IV of tRNA. The EF[elongation factor]-T dependent binding of Phe-tRNA to ribosomes (in the presence of GTP or GMPPCP) and the GTPase activity associated with EF-T dependent binding of the Phe-tRNA were inhibited by C-A-Phe, C-A(2''Phe)H, and C-A(2''H)Phe. These aminoacyl oligonucleotides inhibit the formation of ternary complex EF-Tu.cntdot.GTP.cntdot.AA-tRNA and the interaction of this complex with the ribosomal A site. The uncoupled EF-Tu dependent GTPase (in the absence of AA-tRNA), was also inhibited by C-A-Phe, C-A(2''Phe)H and C-A(2''H)Phe, while nonenzymatic binding of Phe-tRNA to the ribosomal A site was inhibited by C-A-Phe and C-A(2''-Phe)H, but not by C-A(2''H)Phe. The tetranucleotide T-.psi.-C-Gp inhibited enzymatic binding of Phe-tRNA and EF-T dependent GTP hydrolysis. Inhibition of the latter reaction occurred at a lower concentration of T-.psi.-C-Gp suggesting a specific role of T-.psi.-C-Gp loop of AA-tRNA in the GTPase reaction. The role of the 2'' and 3'' isomers of AA-tRNA during enzymatic binding to ribosomes is discussed, and it is suggested that 2'' .fwdarw. 3'' transacylation in AA-tRNA is a step which follows GTP hydrolysis but precedes peptide bond formation.