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J. Biochem, 1974, Vol. 76, No. 4 801-809
© 1974 Japanese Biochemical Society

research-article

Interactions between Elongation Factor Tu.Guanosine Triphosphate and Ribosomes and the Role of Ribosome-bound Transfer RNA in Guanosine Triphosphatase Reaction

Masao KAWAKITA, Ken-ichi ARAI and Yoshito KAZIRO

Institute of Medical Science, University of Tokyo Takanawa, Minato-ku, Tokyo

EF-Tu.GTP, but not EF-Tu.GDP, was shown to interact with uncomplexed ribosomes since only the former was protected by ribosomes against inactivation by N-ethylmaleimide. However, the GTP moiety of EF-Tu.GTP was hardly hydrolyzed, indicating that the catalytic site for GTP splitting is not active in uncomplexed ribosomes.

On the other hand, the interaction of EF-Tu.GTP with ribosomal complexes carrying N-acetylphenylalanyl-tRNA or phenylalanyl-tRNA in the A site was found to lead to GTP splitting. Presumably the catalytic site for GTP splitting is activated when the A site has been occupied by appropriate tRNA ligands. However, this interaction and GTP splitting, which is uncoupled from phenylalanyl-tRNA binding, were observed only when ribosomal peptidyl transferase was inactive. On reactivation of peptidyl transferase the uncoupled GTP splitting was abolished. It is suggested that the interaction of EF-Tu.GTP with ribosomal complexes carrying either N-acetylphenylalanyl-tRNA or phenylalanyl-tRNA on the A site was eliminated in so far as their peptidyl transferase activity is retained in the active state.

From these observations it was concluded that a tight coupling of EF-Tu-dependent GTPase under physiological conditions is dependent on ligand(tRNA)-induced activation of the catalytic site on ribosomes, and also on ligand-induced change in the affinity of ribosomes toward EF-Tu. Both are probably mediated through a ligand-induced conformational alteration of ribosomes.


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