Structure and structural variations of the Escherichia coli 30 S ribosomalsubunit as revealed by three-dimensional cryo-electron microscopy

A three-dimensional reconstruction of the 30 S subunit of the Escherichia c oli ribosome was obtained at 23 Angstrom resolution. Because of the improve d resolution, many more structural details are seen as compared to those ob tained in earlier studies. Thus, the new structure is more suitable for com parison with the 30 S subunit part of the 70 S ribosome, whose structure is already known at a better resolution. In addition, we observe relative and , to some extent, independent movements of three main structural domains of the 30 S subunit, namely head, platform and the main body, which lead to p artial blurring of the reconstructed volume. An attempt to subdivide the da ta set into conformationally defined subsets reveals the existence of confo rmers in which these domains have different orientations with respect to on e another. This result suggests the existence of dynamic properties of the 30 S subunit that might be required for facilitating its interactions with mRNA, tRNA and other ligands during protein biosynthesis. (C) 1999 Academic Press.