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© The Rockefeller University Press, 0021-9525/1998//675 $5.00
The Journal of Cell Biology, Volume 141, Number 3, , 1998 675-687

Articles

Xgrip109: A {gamma} Tubulin–Associated Protein with an Essential Role in {gamma} Tubulin Ring Complex ({gamma}TuRC) Assembly and Centrosome Function



Ona C. Martin*, Ruwanthi N. Gunawardane*, Akihiro Iwamatsu{ddagger}, and Yixian Zheng*

* Department of Embryology, Carnegie Institution of Washington, Baltimore, Maryland 21210; and {ddagger} Central Laboratories for Key Technology, Kirin Brewery Company, Ltd., Yokohama 236, Japan

Previous studies indicate that {gamma} tubulin ring complex ({gamma}TuRC) can nucleate microtubule assembly and may be important in centrosome formation. {gamma}TuRC contains approximately eight subunits, which we refer to as Xenopus gamma ring proteins (Xgrips), in addition to {gamma} tubulin. We found that one {gamma}TuRC subunit, Xgrip109, is a highly conserved protein, with homologues present in yeast, rice, flies, zebrafish, mice, and humans. The yeast Xgrip109 homologue, Spc98, is a spindle–pole body component that interacts with {gamma} tubulin. In vertebrates, Xgrip109 identifies two families of related proteins. Xgrip109 and Spc98 have more homology to one family than the other. We show that Xgrip109 is a centrosomal protein that directly interacts with {gamma} tubulin. We have developed a complementation assay for centrosome formation using demembranated Xenopus sperm and Xenopus egg extract. Using this assay, we show that Xgrip109 is necessary for the reassembly of salt-disrupted {gamma}TuRC and for the recruitment of {gamma} tubulin to the centrosome. Xgrip109, therefore, is essential for the formation of a functional centrosome.

Abbreviations used in this paper: {gamma}TuRC, {gamma} tubulin ring complex; Xgrip, Xenopus gamma ring protein; Asp, ammonium sulfate pellet; CSF, cytostatic factor; DAPI, 4',6-diamidino-2-phenylindole; EST, expressed sequence tag; GST, glutathione S-transferase; MTOC, microtubule organizing center; ORF, open reading frame; PCM, pericentriolar material; PEG, polyethylene glycol.

The cloning of Xgrip109 was initiated in the Alberts lab (University of California, San Francisco, CA). We thank T. Hirano (Cold Spring Harbor Laboratory, Cold Spring Harbor, NY) for his advice on the library screen and Z. Wu and J. Gall (both from Carnegie Institution of Washington, Baltimore, MD) for the Xenopus tissue culture cell line. We are grateful to T. Mitchison (Harvard University, Cambridge, MA) for his advice and help with the initial {gamma}TuRC purification and characterization. We thank K. Oogema (Harvard University, Cambridge, MA) C. Wiese, C.-M. Fan, O. Cohen-Fix, and D. Koshland (all four from Carnegie Institution of Washington) for their critical comments on the manuscript.

Address all correspondence to Yixian Zheng, Department of Embryology, Carnegie Institution of Washington, 115 West University Parkway, Baltimore, MD 21210. Tel.: (410) 554-1232. Fax: (410) 243-6311. E-mail: zheng{at}mail1.ciwemb.edu


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