Conformational variability in Escherichia coli 70S ribosome as revealed by3D cryo-electron microscopy

During protein biosynthesis, ribosomes are believed to go through a cycle o f conformational transitions. We have identified some of the most variable regions of the E. coli 70S ribosome and its subunits, by means of cryo-elec tron microscopy and three-dimensional (3D) reconstruction. Conformational c hanges in the smaller 30S subunit are mainly associated with the functional ly important domains of the subunit, such as the neck and the platform, as seen by comparison of heal-activated, non-activated and SOS-bound states. I n the larger 50S subunit the most variable regions are the L7/L12 stalk, ce ntral protuberance and the L1-protein, as observed in various tRNA-70S ribo some complexes. Difference maps calculated between 3D maps of ribosomes hel p pinpoint the location of ribosomal regions that are most strongly affecte d by conformational transitions. These results throw direct light on the dy namic behavior of the ribosome and help in understanding the role of these flexible domains in the translation process. (C) 1999 Elsevier Science Ltd. All rights reserved.