The stoichiometry of ribosomal translocation.

Fusidic acid does not inhibit the translocation of N-acetylphenylalanyl-tRNA (N-acetyl-Phe-tRNA), bound nonenzymitally to the ribosomal A-site, when the amount of ribosomes in the reaction mixture is not sufficient to trap all the available elongation factor G (EF-G) in the form of GDP ‘EF-G .fusidic acid .ribosome complexes. Moreover, since only those ribosomes in the reaction mixture that are devoid of N-acetylPhe-tRNA form this complex, their strong, uncoupled EF G-dependent GTP hydrolysis is inhibited by the presence of the complex, and the GTP hydrolysis associated with translocation of the fraction of ribosomes charged with N-acetylPhe-tRNA can be detected. After correction for the limited hydrolysis due to the formation of the GDP.EF-G.fusidic acid .ribosome complex on the uncharged ribosomes, it is found that 1 molecule of GTP is hydrolyzed per molecule of N-acetyl-Phe-tRNA translocated.