title: An extended γ-tubulin ring functions as a stable platform in microtubule nucleation.
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.
authors.affiliation: Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, 69120 Heidelberg, Germany.
authors.forename: Sarah
authors.initials: S
authors.lastname: Erlemann
authors.forename: Annett
authors.initials: A
authors.lastname: Neuner
authors.forename: Linda
authors.initials: L
authors.lastname: Gombos
authors.forename: Romain
authors.initials: R
authors.lastname: Gibeaux
authors.forename: Claude
authors.initials: C
authors.lastname: Antony
authors.forename: Elmar
authors.initials: E
authors.lastname: Schiebel
mesh_terms: D002453:Cell Cycle; D003593:Cytoplasm / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism; D014404:Tubulin / Q000378:metabolism*
chemical_list: D014404:Tubulin