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The γ-tubulin ring complex (γTuRC) is the primary microtubule nucleator in cells. γTuRC is assembled from repeating γ-tubulin small complex (γTuSC) subunits and is thought to function as a template by presenting a γ-tubulin ring that mimics microtubule geometry. However, a previous yeast γTuRC structure showed γTuSC in an open conformation that prevents matching to microtubule symmetry. By contrast, we show here that γ-tubulin complexes are in a closed conformation when attached to microtubules. To confirm the functional importance of the closed γTuSC ring, we trapped the closed state and determined its structure, showing that the γ-tubulin ring precisely matches microtubule symmetry and providing detailed insight into γTuRC architecture. Importantly, the closed state is a stronger nucleator, thus suggesting that this conformational switch may allosterically control γTuRC activity. Finally, we demonstrate that γTuRCs have a strong preference for tubulin from the same species.


Justin M Kollman, Charles H Greenberg, Sam Li, Michelle Moritz, Alex Zelter, Kimberly K Fong, Jose-Jesus Fernandez, Andrej Sali, John Kilmartin, Trisha N Davis, David A Agard. Ring closure activates yeast γTuRC for species-specific microtubule nucleation. Nature structural & molecular biology. 2015 Feb;22(2):132-7

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PMID: 25599398

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