A MODEL OF THE TRANSLATIONAL APPARATUS BASED ON A 3-DIMENSIONAL RECONSTRUCTION OF THE ESCHERICHIA-COLI RIBOSOME

The morphology of the Escherichia coli ribosome, i.e., its shape at mo derate to low (20-40 Angstrom (1 Angstrom = 0.1 nm)) resolution, provi des important constraints in modeling both the folding of ribosomal RN A and the translational process. A new reconstruction, obtained by low -dose cryoelectron microscopy and image processing of single ribosomes , contains clues to the way in which the ribosome interacts with the k ey functional ligands: the mRNA and the A- and P-site tRNAs. It also s uggests possible pathways of the nascent polypeptide chain. From an in terpretation of these clues in the light of existing knowledge, a plau sible model for the locations and interactions of key components of pr otein synthesis is suggested.