title: Blocking site-to-site translocation of a misactivated amino acid by mutation of a class I tRNA synthetase.
abstract: The genetic code is established by the aminoacylation reactions of tRNA synthetases. Its accuracy depends on editing reactions that prevent amino acids from being assigned to incorrect codons. A group of class I synthetases share a common insertion that encodes a distinct site for editing that is about 30 A from the active site. Both misactivated aminoacyl adenylates and mischarged amino acids attached to tRNA are translocated to this site, which, in turn, is divided into subsites--one for the adenylate and one for the aminoacyl moiety attached to tRNA. Here we report that a specific mutation in isoleucyl-tRNA synthetase prevents editing by blocking translocation. The mutation alters a widely conserved residue that is believed to tether the amino group of mischarged tRNA to its subsite for editing. These and other data support a model where editing is initiated by translocation of the misacylated amino acid attached to tRNA to create an "editing complex" that facilitates subsequent rounds of editing by translocation of the misactivated adenylate.
authors.affiliation: The Skaggs Institute for Chemical Biology, The Scripps Research Institute, Beckman Center, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
authors.forename: Anthony C
authors.initials: AC
authors.lastname: Bishop
authors.forename: Tyzoon K
authors.initials: TK
authors.lastname: Nomanbhoy
authors.forename: Paul
authors.initials: P
authors.lastname: Schimmel
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D001693:Biological Transport, Active / Q000235:genetics; D007533:Isoleucine-tRNA Ligase / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D017393:RNA Editing; D012355:RNA, Transfer, Ile / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D016963:Thermus thermophilus / Q000201:enzymology / Q000235:genetics
chemical_list: D012355:RNA, Transfer, Ile; D007533:Isoleucine-tRNA Ligase