Intermediate states in the movement of transfer RNA in the ribosome.

Direct chemical 'footprinting' shows that translocation of transfer RNA occurs in two discrete steps. During the first step, which occurs spontaneously after the formation of the peptide bond, the acceptor end of tRNA moves relative to the large ribosomal subunit resulting in 'hybrid states' of binding. During the second step, which is promoted by elongation factor EF-G, the anticodon end of tRNA, along with the messenger RNA, moves relative to the small ribosomal subunit.