Fig. 3.

Proposed order of dynamic structural events during mRNA translocation. Rates of rotation of the head and body of the 30S subunit, based on FRET experiments and fluorescence quenching of pyrene-labeled mRNA, are from this work (Table 1) and from ref. (19). The nonrotated state is equivalent to the classical state and the body rotated state is equivalent to the hybrid state. Although the rate of mRNA quenching matches the rate of reverse (clockwise) head rotation, translocation of mRNA most likely occurs during forward head rotation, as discussed in the text.