The two subunit ribosome (yellow) is shown bound to tRNA (blue) and mRNA (green). The three states observed, classified as classical, hybrid state-1, and hybrid state-2, are defined by the motions of tRNA acceptor stems with respect to the large subunit. The apparent rates of transition between states are identified as tabulated in Table 1 and Supplemental Table 3. Conformational changes of the ribosome that may be important to tRNA motions, as described in the text, are shown as changes in A, P, and E site color.