Translocation promoted by EF-G binding and GTP hydrolysis. In the third step of elongation, the hybrid binding state formed in the peptidyl transferase reaction (see Figure 18-24) is resolved by the binding of EF-G–GTP at the A site. GTP hydrolysis causes a conformational change in EF-G that displaces the A-site peptidyl-tRNA into the P site, causing the ribosome to move forward by one codon on the mRNA. Once EF-G–GDP is released, the A site is available for another aminoacyl-tRNA.