Microtubule nucleating gamma-TuSC assembles structures with 13-fold microtubule-like symmetry

Nature. 2010 Aug 12;466(7308):879-82. doi: 10.1038/nature09207. Epub 2010 Jul 14.


Microtubules are nucleated in vivo by gamma-tubulin complexes. The 300-kDa gamma-tubulin small complex (gamma-TuSC), consisting of two molecules of gamma-tubulin and one copy each of the accessory proteins Spc97 and Spc98, is the conserved, essential core of the microtubule nucleating machinery. In metazoa multiple gamma-TuSCs assemble with other proteins into gamma-tubulin ring complexes (gamma-TuRCs). The structure of gamma-TuRC indicated that it functions as a microtubule template. Because each gamma-TuSC contains two molecules of gamma-tubulin, it was assumed that the gamma-TuRC-specific proteins are required to organize gamma-TuSCs to match 13-fold microtubule symmetry. Here we show that Saccharomyces cerevisiae gamma-TuSC forms rings even in the absence of other gamma-TuRC components. The yeast adaptor protein Spc110 stabilizes the rings into extended filaments and is required for oligomer formation under physiological buffer conditions. The 8-A cryo-electron microscopic reconstruction of the filament reveals 13 gamma-tubulins per turn, matching microtubule symmetry, with plus ends exposed for interaction with microtubules, implying that one turn of the filament constitutes a microtubule template. The domain structures of Spc97 and Spc98 suggest functions for conserved sequence motifs, with implications for the gamma-TuRC-specific proteins. The gamma-TuSC filaments nucleate microtubules at a low level, and the structure provides a strong hypothesis for how nucleation is regulated, converting this less active form to a potent nucleator.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Buffers
  • Calmodulin-Binding Proteins
  • Cryoelectron Microscopy
  • Cytoskeletal Proteins / chemistry
  • Cytoskeletal Proteins / metabolism
  • Microtubule-Associated Proteins / chemistry
  • Microtubule-Associated Proteins / metabolism
  • Microtubules / chemistry*
  • Microtubules / metabolism
  • Microtubules / ultrastructure*
  • Models, Biological
  • Models, Molecular
  • Multiprotein Complexes / chemistry
  • Multiprotein Complexes / metabolism
  • Multiprotein Complexes / ultrastructure
  • Nuclear Proteins / chemistry
  • Nuclear Proteins / metabolism
  • Saccharomyces cerevisiae / chemistry
  • Saccharomyces cerevisiae / cytology*
  • Saccharomyces cerevisiae / ultrastructure*
  • Saccharomyces cerevisiae Proteins / chemistry
  • Saccharomyces cerevisiae Proteins / metabolism
  • Tubulin / chemistry*
  • Tubulin / metabolism
  • Tubulin / ultrastructure*


  • Buffers
  • Calmodulin-Binding Proteins
  • Cytoskeletal Proteins
  • Microtubule-Associated Proteins
  • Multiprotein Complexes
  • Nuclear Proteins
  • SPC110 protein, S cerevisiae
  • SPC97 protein, S cerevisiae
  • SPC98 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Tubulin