ESCHERICHIA-COLI 70-S RIBOSOME AT 15 ANGSTROM RESOLUTION BY CRYOELECTRON MICROSCOPY - LOCALIZATION OF FMET-TRNA(F)(MET) AND FITTING OF L1 PROTEIN

Cryo-electron microscopy of the ribosome in different binding states w ith mRNA and tRNA helps unravel the different steps of protein synthes is. Using over 29,000 projections of a ribosome complex in single-part icle form, a three-dimensional map of the Escherichia coli 70 S riboso me was obtained in which a single site, the P site, is occupied by fMe t-tRNA(f)(Met) as directed by an AUG codon containing mRNA. The superi or resolution of this three-dimensional map, 14.9 Angstrom, has made i t possible to fit the tRNA X-ray crystal structure directly and unambi guously into the electron density, thus determining the locations of a nticodon-codon interaction and peptidyltransferase center of the ribos ome. Furthermore, at this resolution, one of the distinctly visible do mains corresponding to a ribosomal protein, L1, closely matches with i ts X-ray structure. (C) 1998 Academic Press.