Structural studies of the translational apparatus

Significant progress is occurring at an accelerated rate in structural stud ies of ribosomes. A 3D cryoelectron microscopy map of the 70S ribosome from Escherichia coli is available at 15 Angstrom resolution and a combination of cryoelectron microscopy with X-ray crystallography has yielded a 9 Angst rom resolution map of the 50S subunit from Haloarcula marismortui, an archa ebacterium. For eukaryotes, 3D cryomaps of the 80S ribosomes from yeast and from mammals have now been produced at resolutions in the range 20 to 30 A ngstrom. The most ground-breaking results have been obtained from the 3D ma pping of ligands in functional studies of prokaryotic ribosomes. These stud ies, which directly visualize the protein synthesis machine in action, have brought new excitement to a field that was relatively dormant during the p ast decade.