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© The Rockefeller University Press,
0021-9525/2000//1525 $5.00
The Journal of Cell Biology, Volume 151, Number 7,
, 2000 1525-1536
Original Article |
The Role of Xgrip210 in 
-Tubulin Ring Complex Assembly and Centrosome Recruitment
zheng{at}ciwemb.edu
The
-tubulin ring complex (TuRC), purified from the cytoplasm of vertebrate and invertebrate cells, is a microtubule nucleator in vitro. Structural studies have shown that TuRC is a structure shaped like a lock-washer and topped with a cap. Microtubules are thought to nucleate from the uncapped side of the TuRC. Consequently, the cap structure of the TuRC 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 TuRC, Xgrip210. We show that Xgrip210 is a conserved centrosomal protein that is essential for the formation of TuRC. Using immunogold labeling, we found that Xgrip210 is localized to the ends of microtubules nucleated by the TuRC and that its localization is more distal, toward the tip of the TuRC-cap structure, than that of -tubulin. Immunodepletion of Xgrip210 blocks not only the assembly of the TuRC, but also the recruitment of -tubulin and its interacting protein, Xgrip109, to the centrosome. These results suggest that Xgrip210 is a component of the TuRC cap structure that is required for the assembly of the TuRC.
Key Words: Xgrip210 • centrosome • microtubule nucleation • -tubulin ring complex • Xenopus
© 2000 The Rockefeller University Press
Dr. Keating's and Dr. Borisy's present address is Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, IL 60611.Abbreviations used in this paper: CSF, cytostatic factor; Dgrip, Drosophila gamma ring protein;
TuRC, -tubulin ring complex; TuSC, -tubulin small complex; MT, microtubule; Xgrip, Xenopus gamma ring protein.
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