Head rotation of the small subunit. Superimposition of atomic models (obtained by real-space refinement) of the bodies of the small subunit of the pre-translocational (tan, PDB code: 1K5X) and the ratcheted, eEF2-bound (blue, PDB code: 1S1H) 80S ribosomes, by explicit least-squares fitting. Highlighted residues U955 and A1339 are in regions known to interact with ribosome-bound A- and P-site tRNAs, respectively. This figure was altered for the purposes of this article. Data adapted from Taylor et al. (2007), copyright (2007) Nature Publishing Group.