Ratchet-like motion and hybrid tRNA configuration. (A) Superimposition of 30S (left) and 50S (right) subunits, as seen from the inter-subunit side. Classic-state subunits are shown in transparent grey, while the subunits of the hybrid-state ribosome are in solid yellow (30S) and blue (50S). (B) Close-up view of the 50S subunit showing the classic tRNA configuration. (C) Close-up view of the 50S subunit showing the hybrid tRNA configuration. The orientations of the subunits are shown as successive thumbnails on the left. Data reproduced from Agirrezabala et al.