title: The elongating ribosome: structural and functional aspects.
abstract: We determined the positions and arrangements of RNA ligands within the ribosome with a new neutron-scattering technique, the proton-spin contrast-variation. Two tRNAs were bound to the ribosome in the pre-translocational and the post-translocational state. The mass centre of gravity of both tRNAs resides at the subunit interface of the body of the 30S subunit. Both tRNAs are separated by an angle of 50-55 degrees, and their mutual arrangement does not change during translocation. The mass centre of gravity moves by 13 +/- 3 A (1A = 0.1 nm) during translocation, corresponding well with the length of one codon. Using an RNase-digestion technique, the length of the mRNA sequence covered by the ribosome was determined to be 39 +/- 3 nucleotides before and after translocation. The ribosome moves like a rigid frame along the mRNA during translocation. In contrast, both tRNAs seem to be located on a movable ribosomal domain, which carries the tRNAs before, during, and after translocation, leaving the microtopography of the tRNAs with the ribosome unaltered. This conclusion was derived from an analysis of the contract patterns of thioated tRNAs on the ribosome. The results have led to a new model of the elongation cycle, which reinterprets the features of the previous "allosteric three-sites model" in a surprisingly simple fashion. Finally, a mutational analysis has identified a single nucleotide of the 23S rRNA essential for the peptidyltransferase activity.
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, AG Ribosomen, Berlin, Germany.
authors.forename: K H
authors.initials: KH
authors.lastname: Nierhaus
authors.forename: D
authors.initials: D
authors.lastname: Beyer
authors.forename: M
authors.initials: M
authors.lastname: Dabrowski
authors.forename: M A
authors.initials: MA
authors.lastname: Schäfer
authors.forename: C M
authors.initials: CM
authors.lastname: Spahn
authors.forename: J
authors.initials: J
authors.lastname: Wadzack
authors.forename: J U
authors.initials: JU
authors.lastname: Bittner
authors.forename: N
authors.initials: N
authors.lastname: Burkhardt
authors.forename: G
authors.initials: G
authors.lastname: Diedrich
authors.forename: R
authors.initials: R
authors.lastname: Jünemann
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010441:Peptide Chain Elongation, Translational; D011522:Protons; D012343:RNA, Transfer / Q000737:chemistry* / Q000502:physiology; D012270:Ribosomes / Q000737:chemistry* / Q000502:physiology; D014178:Translocation, Genetic
chemical_list: D011522:Protons; D012343:RNA, Transfer