Solution structure of the E. coli 70S ribosome at 11.5 angstrom resolution

Over 73,000 projections of the E. coli ribosome bound with formyl-methionyl initiator tRNA(f)(Met) were used to obtain an 11.5 Angstrom cryo-electron microscopy map of the complex. This map allows identification of RNA helice s, peripheral proteins, and intersubunit bridges. Comparison of double-stra nded RNA regions and positions of proteins identified in both cryo-EM and X -ray maps indicates good overall agreement but points to rearrangements of ribosomal components required for the subunit association. Fitting of known components of the 50S stalk base region into the map defines the architect ure of the GTPase-associated center and reveals a major change in the orien tation of the alpha-sarcin-ricin loop. Analysis of the bridging connections between the subunits provides insight into the dynamic signaling mechanism between the ribosomal subunits.