title: Structure of the gamma-tubulin ring complex: a template for microtubule nucleation.
abstract: The gamma-tubulin ring complex (gammaTuRC) is a protein complex of relative molecular mass approximately 2.2 x 10(6) that nucleates microtubules at the centrosome. Here we use electron-microscopic tomography and metal shadowing to examine the structure of isolated Drosophila gammaTuRCs and the ends of microtubules nucleated by gammaTuRCs and by centrosomes. We show that the gammaTuRC is a lockwasher-like structure made up of repeating subunits, topped asymmetrically with a cap. A similar capped ring is also visible at one end of microtubules grown from isolated gammaTuRCs and from centrosomes. Antibodies against gamma-tubulin label microtubule ends, but not walls, in centrosomes. These data are consistent with a template-mediated mechanism for microtubule nucleation by the gammaTuRC.
authors.affiliation: Department of Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, 513 Parnassus Avenue, San Francisco, California 94143, USA. moritz@msg.ucsf.edu
authors.forename: M
authors.initials: M
authors.lastname: Moritz
authors.forename: M B
authors.initials: MB
authors.lastname: Braunfeld
authors.forename: V
authors.initials: V
authors.lastname: Guénebaut
authors.forename: J
authors.initials: J
authors.lastname: Heuser
authors.forename: D A
authors.initials: DA
authors.lastname: Agard
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology; D001704:Biopolymers / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D018385:Centrosome / Q000737:chemistry / Q000276:immunology / Q000378:metabolism / Q000648:ultrastructure; D004331:Drosophila melanogaster; D008854:Microscopy, Electron; D008870:Microtubules / Q000737:chemistry / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure*; D008954:Models, Biological; D008970:Molecular Weight; D010984:Platinum; D011233:Precipitin Tests; D020836:Protein Structure, Quaternary; D016628:Replica Techniques; D016626:Shadowing Technique, Histology; D014404:Tubulin / Q000737:chemistry / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure*
chemical_list: D000906:Antibodies; D001704:Biopolymers; D014404:Tubulin; D010984:Platinum