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J Cell Biol. 2012 Apr 2;197(1):59-74. doi: 10.1083/jcb.201111123.

An extended γ-tubulin ring functions as a stable platform in microtubule nucleation.

Author information

  • 1Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, 69120 Heidelberg, Germany.

Abstract

γ-Tubulin complexes are essential for microtubule (MT) nucleation. The γ-tubulin small complex (γ-TuSC) consists of two molecules of γ-tubulin and one molecule each of Spc97 and Spc98. In vitro, γ-TuSCs oligomerize into spirals of 13 γ-tubulin molecules per turn. However, the properties and numbers of γ-TuSCs at MT nucleation sites in vivo are unclear. In this paper, we show by fluorescence recovery after photobleaching analysis that γ-tubulin was stably integrated into MT nucleation sites and was further stabilized by tubulin binding. Importantly, tubulin showed a stronger interaction with the nucleation site than with the MT plus end, which probably provides the basis for MT nucleation. Quantitative analysis of γ-TuSCs on single MT minus ends argued for nucleation sites consisting of approximately seven γ-TuSCs with approximately three additional γ-tubulin molecules. Nucleation and anchoring of MTs required the same number of γ-tubulin molecules. We suggest that a spiral of seven γ-TuSCs with a slight surplus of γ-tubulin nucleates MTs in vivo.

PMID:
22472440
[PubMed - indexed for MEDLINE]
PMCID:
PMC3317808
Free PMC Article

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