Structural studies of the translational apparatus.

Significant progress is occurring at an accelerated rate in structural studies of ribosomes. A 3D cryoelectron microscopy map of the 70S ribosome from Escherichia coli is available at 15 A resolution and a combination of cryoelectron microscopy with X-ray crystallography has yielded a 9 A resolution map of the 50S subunit from Haloarcula marismortui, an archaebacterium. 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. The most ground-breaking results have been obtained from the 3D mapping of ligands in functional studies of prokaryotic ribosomes. These studies, which directly visualize the protein synthesis machine in action, have brought new excitement to a field that was relatively dormant during the past decade.