title: Intersubunit movement is required for ribosomal translocation.
abstract: Translocation of tRNA and mRNA during protein synthesis is believed to be coupled to structural changes in the ribosome. The "ratchet model," based on cryo-EM reconstructions of ribosome complexes, invokes relative movement of the 30S and 50S ribosomal subunits in this process; however, evidence that directly demonstrates a requirement for intersubunit movement during translocation is lacking. To address this problem, we created an intersubunit disulfide cross-link to restrict potential movement. The cross-linked ribosomes were unable to carry out polypeptide synthesis; this inhibition was completely reversed upon reduction of the disulfide bridge. In vitro assays showed that the cross-linked ribosomes were specifically blocked in elongation factor G-dependent translocation. These findings show that intersubunit movement is required for ribosomal translocation, accounting for the universal two-subunit architecture of ribosomes.
authors.affiliation: Department of Molecular, Cell, and Developmental Biology and Center for Molecular Biology of RNA, University of California, Santa Cruz, CA 95064, USA.
authors.forename: Lucas H
authors.initials: LH
authors.lastname: Horan
authors.forename: Harry F
authors.initials: HF
authors.lastname: Noller
mesh_terms: D001483:Base Sequence; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004220:Disulfides / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020653:Peptide Elongation Factor G / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism*
chemical_list: D003432:Cross-Linking Reagents; D004220:Disulfides; D020653:Peptide Elongation Factor G; D012333:RNA, Messenger