title: Molecular mechanics of 30S subunit head rotation.
abstract: During ribosomal translocation, a process central to the elongation phase of protein synthesis, movement of mRNA and tRNAs requires large-scale rotation of the head domain of the small (30S) subunit of the ribosome. It has generally been accepted that the head rotates by pivoting around the neck helix (h28) of 16S rRNA, its sole covalent connection to the body domain. Surprisingly, we observe that the calculated axis of rotation does not coincide with the neck. Instead, comparative structure analysis across 55 ribosome structures shows that 30S head movement results from flexing at two hinge points lying within conserved elements of 16S rRNA. Hinge 1, although located within the neck, moves by straightening of the kinked helix h28 at the point of contact with the mRNA. Hinge 2 lies within a three-way helix junction that extends to the body through a second, noncovalent connection; its movement results from flexing between helices h34 and h35 in a plane orthogonal to the movement of hinge 1. Concerted movement at these two hinges accounts for the observed magnitudes of head rotation. Our findings also explain the mode of action of spectinomycin, an antibiotic that blocks translocation by binding to hinge 2.
authors.affiliation: Center for Molecular Biology of RNA and Department of Molecular, Cell, and Developmental Biology, University of California at Santa Cruz, Santa Cruz, CA 95064.
authors.forename: Srividya
authors.initials: S
authors.lastname: Mohan
authors.affiliation: Center for Molecular Biology of RNA and Department of Molecular, Cell, and Developmental Biology, University of California at Santa Cruz, Santa Cruz, CA 95064.
authors.forename: John Paul
authors.initials: JP
authors.lastname: Donohue
authors.affiliation: Center for Molecular Biology of RNA and Department of Molecular, Cell, and Developmental Biology, University of California at Santa Cruz, Santa Cruz, CA 95064 harry@nuvolari.ucsc.edu.
authors.forename: Harry F
authors.initials: HF
authors.lastname: Noller
mesh_terms: D001483:Base Sequence; D004926:Escherichia coli / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D012336:RNA, Ribosomal, 16S / Q000737:chemistry; D054657:Ribosome Subunits / Q000737:chemistry*; D012399:Rotation; D000198:Spectinomycin / Q000737:chemistry / Q000378:metabolism; D016963:Thermus thermophilus / Q000378:metabolism
chemical_list: D012336:RNA, Ribosomal, 16S; D000198:Spectinomycin
keywords: RNA dynamics; S5; three-way junction; translation