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Article
Nature Cell Biology 2, 365–370 (1 June 2000) | doi:10.1038/35014058
Structure of the |[ggr]|-tubulin ring complex: a template for microtubule nucleation
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Abstract
The |[ggr]|-tubulin ring complex (|[ggr]|TuRC) is a protein complex of relative molecular mass ~2.2 |[times]| 106 that nucleates microtubules at the centrosome. Here we use electron-microscopic tomography and metal shadowing to examine the structure of isolated Drosophila |[ggr]|TuRCs and the ends of microtubules nucleated by |[ggr]|TuRCs and by centrosomes. We show that the |[ggr]|TuRC 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 |[ggr]|TuRCs and from centrosomes. Antibodies against |[ggr]|-tubulin label microtubule ends, but not walls, in centrosomes. These data are consistent with a template-mediated mechanism for microtubule nucleation by the |[ggr]|TuRC.
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