LAUSR

Significance Using ensemble FRET, we measured the effects of inhibition of GTP hydrolysis on rotational movements of the 30S ribosomal subunit and of the head domain of the 30S subunit during ribosomal translocation. Surprisingly, we find that blockage of GTP hydrolysis by the elongation factor G (EF-G) specifically abolishes reverse rotation of the head domain of the small ribosomal subunit, an event that occurs after translocation of the transfer RNA and messenger RNA is essentially complete. We propose that the principal role of GTP hydrolysis is to ensure that EF-G is not released from the ribosome until completion of each round of translocation, which guards against slippage of the translational reading frame.