γ-tubulin complexes: binding to the centrosome, regulation and microtubule nucleation

Abstract

Microtubule assembly is initiated in vivo by γ-tubulin complexes. Cytoplasmic γ-tubulin complexes are targeted to centrosomes or to other microtubule organizing centers (MTOCs) via a set of so called γ-tubulin complex binding proteins (GTBPs) that probably interact with the conserved Spc97p/Spc98p protein family of γ-tubulin complexes. In other cell types, γ-tubulin complexes may initiate microtubule formation near chromosomes in a MTOC-independent manner. Recently, major advances have been achieved through the finding that γ-tubulin, Spc97p and Spc98p form a conserved core that is probably responsible for microtubule nucleation, and by the discovery that a yeast GTBP is regulated in a cell-cycle-dependent manner and in response to an external signal. Furthermore, it was found that the small GTPase Ran in its GDP-bound state may promote spindle assembly. In addition, an essential function of γ-tubulin in basal body duplication has been demonstrated in Paramecium.