title: Immunostructural evidence for the template mechanism of microtubule nucleation.
abstract: Two opposing models have been proposed to explain how the gamma-tubulin ring complex (gammaTuRC) induces microtubule nucleation. In the 'protofilament' model, the gammaTuRC induces nucleation as a partially or completely straightened protofilament that is incorporated longitudinally into the wall of the nascent microtubule, whereas the 'template' model proposes that the gammaTuRC acts as a helical template that constitutes the base of the newly-formed polymer. Here we appraise these two models, using high-resolution structural and immunolocalization methods. We show that components of the gammaTuRC localize to a narrow zone at the extreme minus end of the microtubule and that these ends terminate in a pointed cap. Together, these results strongly favour the template model of microtubule nucleation.
authors.affiliation: Laboratory of Molecular Biology, University of Wisconsin, Madison, Wisconsin 53706, USA. tkeating@facstaff.wisc.edu
authors.forename: T J
authors.initials: TJ
authors.lastname: Keating
authors.forename: G G
authors.initials: GG
authors.lastname: Borisy
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology; D001704:Biopolymers / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D002498:Centrifugation; D006046:Gold; D016547:Kinesins / Q000235:genetics / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D008870:Microtubules / Q000737:chemistry / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure*; D008954:Models, Biological; D010984:Platinum; D020836:Protein Structure, Quaternary; D016628:Replica Techniques; D014404:Tubulin / Q000737:chemistry / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure*; D014982:Xenopus laevis
chemical_list: D000906:Antibodies; D001704:Biopolymers; D014404:Tubulin; D010984:Platinum; D006046:Gold; D016547:Kinesins