Figure 3.

Schematic representation of Model III ⁸. From the posttranslocation state (State POST1), deacylated tRNA dissociates rapidly and the aminoacyl-tRNA.EF-Tu.GTP ternary complex binds in the initial A/T state (State A/T). Upon accommodation of the aminoacyl-tRNA (State A/A), the tRNA of the A site is twisted, and as a result, the anticodon and the associated mRNA are displaced by 9 Å into the entry channel of the ribosome, unwinding an mRNA base pair. After the peptidyl transfer (State C), the stress in the mRNA is released. Then, EF-G.GTP of saturating concentration binds immediately, facilitating the classical non-rotated pretranslocation state transition to hybrid state. GTP hydrolysis to GDP.Pi in hybrid state induces the ribosomal unlocking, opening the mRNA channel (State H). The subsequent reverse intersubunit rotation causes the small ribosomal 30S subunit translocating forward by unwinding three mRNA base pairs, with State H transiting to State POST2, from which the next elongation cycle continues.