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Immunostructural evidence for the template mechanism of microtubule nucleation

Nature Cell Biology volume 2, pages 352–357 (2000)Cite this article

Abstract

Two opposing models have been proposed to explain how the γ-tubulin ring complex (γTuRC) induces microtubule nucleation. In the ‘protofilament’ model, the γTuRC 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 γTuRC 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 γTuRC 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.

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Figure 1: Light microscopic visualization of γ-TuRC components at the ends of single microtubules.
Figure 2: Ultrastructural localization of γ-TuRC components at microtubule ends.
Figure 3: Distribution of γ-TuRC components and comparison to predictions of the template and protofilament models of microtubule nucleation.
Figure 4: Models of the microtubule-nucleating and -capping structure.

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Acknowledgements

We thank C. Echeverri and R. Vallee for the p50/dynamitin construct, R. Vale and F. McNally for the hKin560-his construct, B. Bement for gravid frogs and T. Svitkina for assistance with electron-microscopy work. We are grateful to B. Bement, J. Peloquin and members of the Borisy laboratory for discussions and advice, to S. Limbach for technical assistance and to L. Olds for help in preparing the figures. This work was supported by a Postdoctoral Fellowship from the American Cancer Society (to T.J.K.) and by NIH grant GM25062 (to G.G.B.).

Correspondence and requests for materials should be addressed to T.J.K.

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  1. Laboratory of Molecular Biology, University of Wisconsin, Madison, Wisconsin, 53706, USA

    Thomas J. Keating & Gary G. Borisy

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Correspondence to Thomas J. Keating.

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Keating, T., Borisy, G. Immunostructural evidence for the template mechanism of microtubule nucleation . Nat Cell Biol 2, 352–357 (2000). https://doi.org/10.1038/35014045

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