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Nat Cell Biol. 2018 May;20(5):575-585. doi: 10.1038/s41556-018-0091-6. Epub 2018 Apr 25.

XMAP215 is a microtubule nucleation factor that functions synergistically with the γ-tubulin ring complex.

Author information

1
Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ, USA.
2
Department of Molecular Biology, Princeton University, Princeton, NJ, USA.
3
Department of Molecular Biology, Princeton University, Princeton, NJ, USA. spetry@princeton.edu.

Abstract

How microtubules (MTs) are generated in the cell is a major question in understanding how the cytoskeleton is assembled. For several decades, γ-tubulin has been accepted as the universal MT nucleator of the cell. Although there is evidence that γ-tubulin complexes are not the sole MT nucleators, identification of other nucleation factors has proven difficult. Here, we report that the well-characterized MT polymerase XMAP215 (chTOG/Msps/Stu2p/Alp14/Dis1 homologue) is essential for MT nucleation in Xenopus egg extracts. The concentration of XMAP215 determines the extent of MT nucleation. Even though XMAP215 and the γ-tubulin ring complex (γ-TuRC) possess minimal nucleation activity individually, together, these factors synergistically stimulate MT nucleation in vitro. The amino-terminal TOG domains 1-5 of XMAP215 bind to αβ-tubulin and promote MT polymerization, whereas the conserved carboxy terminus is required for efficient MT nucleation and directly binds to γ-tubulin. In summary, XMAP215 and γ-TuRC together function as the principal nucleation module that generates MTs in cells.

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