3-DIMENSIONAL RECONSTRUCTION OF THE ESCHERICHIA-COLI 30-S RIBOSOMAL-SUBUNIT IN ICE

Three-dimensional (3D) reconstructions of both the heat-activated and non-activated 30 S subunit of the Escherichia coli 70 S ribosome were obtained from a frozen hydrated specimen preparation at 1/37 Angstrom( -1) resolution. Well-characterized features that can be identified in both reconstructions are the head, the base, the platform and the clef t formed between the head and the platform. Comparisons between the 3D maps of 30 S subunits at 0 degrees C, heat-activated at 37 degrees C, and the 30 S subunit portion identified in the cryo-3D map of 70 S ri bosome reveal conformational changes the subunit probably undergoes du ring inactive-active transition and upon association with the 50 S sub unit. These comparisons also allow us to localize the sites of associa tion of 30 S and 50 S subunits. (C) 1996 Academic Press Limited