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. Author manuscript; available in PMC: 2010 Mar 5.
Published in final edited form as: Q Rev Biophys. 2009 Aug;42(3):159–200. doi: 10.1017/S0033583509990060

Fig. 23.

Fig. 23

A model for EF-G based translocation. Once the incoming aa-tRNA is incorporated and the peptide transferred, the pre-translocational ribosomes starts fluctuating between (a) the classic (MSI) and (b) the hybrid tRNA configuration (MSII), a rearrangement coupled to the ratcheting of the small subunit. (c) The binding of EF-G stabilizes the ratcheted, MSII conformation of the ribosome. (d) Hydrolysis of GTP promotes the shift of domain IV of EF-G, which in turn detaches the mRNA–tRNA complex from the decoding center and allows rotation of the head. (e) The head rotation translocates the hybrid tRNAs to the P and E sites. (f) Translocation is completed by back-rotation of the head and reverse-ratcheting of the entire small subunit as EF-G in its GDP form is released from the ribosome.