Molecular recognition and catalysis in translation termination complexes.

When the ribosome machinery reaches a stop codon in the mRNA, protein synthesis stops, and nascent polypeptide release is catalysed by class-I release factors (RFs); class-II RFs then promote the release of class-I RFs. Cryo electron microscopy structures of termination complexes and crystal structures of isolated factors have provided insights into key concepts such as bridging of active sites on the ribosome, and conformational changes that regulate the termination process. Recent crystal structures of the four possible functional ribosome complexes that contain the class-I RFs and the three stop codons have uncovered the molecular mechanisms by which RF1/RF2 (i) both recognise UAA, but discriminate specifically between UAG and UGA, and (ii) catalyse peptide release. Moreover, ongoing research also promises to reveal the structure-function relations of class-II RFs.