In this study, we challenge current ideas about the mechan- ism of translocation. The paradigm shift we propose follows from our observations that intracellular EF-G is likely to be in the GDP-bound form, that the GDP form of the factor can rapidly enter the preT ribosome complex, and that the preT ribosome acts as the GEF for EF-G, similar to the way that the post-termination ribosome acts as the GEF for the peptide-release factor RF3 [9,10]. Our results, partially based on the use of A-site-specific cleavage of mRNA by the bacterial toxin RelE [11] to monitor the position of the mRNA at various translocation steps, show that the exchange of GDP for the non-cleavable GTP analog GDPNP on EF-G bound to the preT complex drives the ribosome into an intermediate translocation state (transT*), wherein the tRNA2-mRNA complex has moved in relation to the 30S subunit. The removal of EF-G•GDPNP from a transT* ribo- some by addition of excess GDP brings the ribosome back to its preT state, while GTP addition brings it to the postT state. From these and previous biochemical data [8], in con- junction with cryo-electron microscopy (cryo-EM) recon- structions of functional ribosomal complexes [5], we provide a mechanistic reinterpretation of the major steps of translocation.