The fourth step of protein synthesis: Disassembly of the posttermination complex

Protein synthesis is generally known as consisting of three steps: initiation, elongation, and termination. Much less known is the fourth step: disassembly of the posttermination ribosomal complex and recycling of the machinery necessary for the next round of translation. In bacteria, after reaching the end of a protein-coding sequence, the ribosome binds release factor RF-1 or RF-2 in response to stop codon in the ribosomal A site, activating hydrolysis of the polypeptide chain from peptidyl-tRNA. Release factor RF-3 then catalyzes dissociation of RF-1 or RF-2, leaving a posttermination complex consisting of the 70S ribosome, mRNA, and deacylated tRNA in the P site. How the posttermination complex is disassembled for next round of protein synthesis is a very basic process. The possible mechanisms of posttermination complex disassembly during protein synthesis was summarized: the forth step of protein synthesis is catalyzed by the concerted action of ribosome recycling factor (RRF) and elongation factor G (EF-G).