Interaction between the ribosome and EF-G; a proposal for the whole mechanism of translocation. (a-c) Release of peptide from the postTerm ribosome allows the intersubunit rotation. (d) EF-G•GDPNP stabilizes the twisted form of the ribosome as observed by cryo-EM . (e-h,k) A model explaining the mechanism of translocation. (i,j) A GTP-analog pathway. The model is explained in detail in the text and symbols are as in Figure 1. L7/12 is a complex of ribosomal proteins thought to activate GTP hydrolysis on ribosomal GTPases. The mauve padlock illustrates states of the ribosome in which the mRNA is locked, and cannot move in relation to the small subunit. Domain IV of EF-G is suggested in the main text to play an important role in translocation.