Microtubule (MT) filaments, composed of alpha/beta-tubulin dimers, are fundamental to cellular architecture, function and organismal development. They are nucleated from MT organizing centers by the evolutionarily conserved gamma-tubulin ring complex (gammaTuRC). However, the molecular mechanism of nucleation remains elusive. Here we used cryo-electron tomography to determine the structure of the native gammaTuRC capping the minus end of a MT in the context of enriched budding yeast spindles. In our structure, gammaTuRC presents a ring of gamma-tubulin subunits to seed nucleation of exclusively 13-protofilament MTs, adopting an active closed conformation to function as a perfect geometric template for MT nucleation. Our cryo-electron tomography reconstruction revealed that a coiled-coil protein staples the first row of alpha/beta-tubulin of the MT to alternating positions along the gamma-tubulin ring of gammaTuRC. This positioning of alpha/beta-tubulin onto gammaTuRC suggests a role for the coiled-coil protein in augmenting gammaTuRC-mediated MT nucleation. Based on our results, we describe a molecular model for budding yeast gammaTuRC activation and MT nucleation.

• PMID: 38609662
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Journal Article

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Dendooven T, Yatskevich S, Burt A, Chen ZA, Bellini D, Rappsilber J, Kilmartin JV, Barford D

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