Termination of translation in bacteria. When the ribosome comes to a stop codon, RF-1 or RF-2 (designated here by RF) binds to the A site and induces release of the polypeptide chain. RF-3–GDP then binds to the ribosome and exchanges GTP for GDP, displacing the RF-1 or RF-2. The RF-3–GTP is tightly bound to the ribosome, but GTP hydrolysis weakens its affinity and RF-3 is released.