The identification of selected components in electron density maps of prokaryotic ribosomes at 7 Å resolution

The MIR map pf the small ribosomal subunit, constructed at 7.2 Å and extended to 5.5 Å using crystals diffracting to 3 Å, shows morphologies close to the active conformation of these particles and contains elongated dense features traceable as RNA chains as well as globular regions in which folds observed in isolated ribosomal proteins were detected. Surface proteins and selected RNA strands are being located by difference Fourier methods, exploiting the metal cluster attached to them.