Release factors and their role as decoding proteins: specificity and fidelity for termination of protein synthesis

The decoding of stop signals in mRNA requires protein release factors. Two classes of factor are found in both prokaryotes and eukaryotes, a decoding factor and a stimulatory recycling factor. These factors form complexes at the active centre of the ribosome and mimic in overall shape the complexes found at other stages of protein synthesis. The decoding release factor is shaped like a tRNA and has a domain for codon recognition at the decoding site of the ribosome, and a domain for peptidyl-tRNA hydrolysis that is inferred to be near the peptidyltransferase centre. Initial interaction of the decoding factor with the ribosome is a low fidelity event involving multiple contacts with the ribosomal components. A subsequent discrimination step, at present poorly defined, ensures high fidelity of codon recognition.