Crystal structures of 70S ribosomes bound to release factors RF1, RF2 and RF3

Termination is a crucial step in translation, most notably because premature termination can lead to toxic truncated polypeptides. Most interesting is the fact that stop codons are read by a completely different mechanism from that of sense codons. In recent years, rapid progress has been made in the structural biology of complexes of bacterial ribosomes bound to translation termination factors, much of which has been discussed in earlier reviews [1, 2, 3, 4 and 5]. Here, we present a brief overview of the structures of bacterial translation termination complexes. The first part summarizes what has been learned from crystal structures of complexes containing the class I release factors RF1 and RF2. In the second part, we discuss the results and implications of two recent X-ray structures of complexes of ribosomes bound to the translational GTPase RF3. These structures have provided many insights and a number of surprises. While structures alone do not tell us how these complicated molecular assemblies work, is it nevertheless clear that it will not be possible to understand their mechanisms without detailed structural information.

► Stop codons are recognized directly by the class I release factors RF1 and RF2.
► Peptidyl-tRNA hydrolysis is catalyzed by the class I release factors themselves.
► The backbone amide nitrogen of the Q in the GGQ motif is involved in catalysis.
► The class II release factor RF3, a GTPase related to EF-G, induces large-scale rotations of the 30S body and head.
► The structure of the RF3·GDPNP·ribosome complex has potential implications for the mechanism of action of EF-G.