Protein tRNA Mimicry in Translation Termination

Termination of protein synthesis takes place on the ribosomes as a response to a stop, rather than a sense,codon in the "decoding" site (A site). Translation termination requires two classes of polypeptide release factors(RFs): a class I factor, codon-specific RFs (RF1 and RF2in prokaryotes; eRF1 in eukaryotes), and a class II factor,nonspecific RFs (RF3 in prokaryotes; eRF3 in eukaryotes) that bind guanine nucleotides and stimulate class IRF activity. Although the termination process and the RFactivity were discovered in vitro in the late 1960s, muchof the mechanism and the apparatus have remained obscure. The underlying mechanism for stop codon decoding represents a longstanding coding problem of considerable interest, since it entails protein–RNA recognitioninstead of the well-understood codon–anticodon pairingduring the mRNA–tRNA interaction. After four decadesof investigation, we are now aware that molecularmimicry between protein and tRNA provides a clue tothis problem...