title: The role of Xgrip210 in gamma-tubulin ring complex assembly and centrosome recruitment.
abstract: The gamma-tubulin ring complex (gammaTuRC), purified from the cytoplasm of vertebrate and invertebrate cells, is a microtubule nucleator in vitro. Structural studies have shown that gammaTuRC is a structure shaped like a lock-washer and topped with a cap. Microtubules are thought to nucleate from the uncapped side of the gammaTuRC. Consequently, the cap structure of the gammaTuRC is distal to the base of the microtubules, giving the end of the microtubule the shape of a pointed cap. Here, we report the cloning and characterization of a new subunit of Xenopus gammaTuRC, Xgrip210. We show that Xgrip210 is a conserved centrosomal protein that is essential for the formation of gammaTuRC. Using immunogold labeling, we found that Xgrip210 is localized to the ends of microtubules nucleated by the gammaTuRC and that its localization is more distal, toward the tip of the gammaTuRC-cap structure, than that of gamma-tubulin. Immunodepletion of Xgrip210 blocks not only the assembly of the gammaTuRC, but also the recruitment of gamma-tubulin and its interacting protein, Xgrip109, to the centrosome. These results suggest that Xgrip210 is a component of the gammaTuRC cap structure that is required for the assembly of the gammaTuRC.
authors.affiliation: Howard Hughes Medical Institute, Carnegie Institution of Washington, Baltimore, Maryland 21210, USA. zheng@ciwemb.edu
authors.forename: L
authors.initials: L
authors.lastname: Zhang
authors.forename: T J
authors.initials: TJ
authors.lastname: Keating
authors.forename: A
authors.initials: A
authors.lastname: Wilde
authors.forename: G G
authors.initials: GG
authors.lastname: Borisy
authors.forename: Y
authors.initials: Y
authors.lastname: Zheng
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D018385:Centrosome / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D003001:Cloning, Molecular; D008297:Male; D008854:Microscopy, Electron; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D011233:Precipitin Tests; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D021122:Protein Subunits; D021381:Protein Transport; D016415:Sequence Alignment; D013094:Spermatozoa / Q000166:cytology / Q000378:metabolism; D014404:Tubulin / Q000378:metabolism*; D029867:Xenopus Proteins; D014982:Xenopus laevis / Q000235:genetics / Q000378:metabolism*
chemical_list: D008869:Microtubule-Associated Proteins; D021122:Protein Subunits; C112307:TUBGCP3 protein, Xenopus; D014404:Tubulin; D029867:Xenopus Proteins; C419560:grip210 protein, Xenopus