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

Microtubule assembly is initiated in vivo by gamma-tubulin complexes. Cytop lasmic gamma-tubulin complexes are targeted to centrosomes or to other micr otubule organizing centers (MTOCs) via a set of so called gamma-tubulin com plex binding proteins (GTBPs) that probably interact with the conserved Spc 97p/Spc98p protein family of gamma-tubulin complexes. In other cell types, gamma-tubulin complexes may initiate microtubule formation near chromosomes in a MTOC-independent manner. Recently, major advances have been achieved through the finding that gamma-tubulin, Spc97p and Spc98p form a conserved core that is probably responsible for microtubule nucleation, and by the di scovery 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 smal l GTPase Ran in its GDP-bound state may promote spindle assembly. In additi on, an essential function of gamma-tubulin in basal body duplication has be en demonstrated in Paramecium.