The γ-TuRC: mastermind of multipurpose actions at the centrosome.

The γ-Tubulin Ring Complex (γ-TuRC) comprised of γ-tubulin and γ-tubulin complex proteins (GCP2-6) serves as the main protein scaffold for microtubule nucleation in most animal cells. In lower eukaryotes such as Saccharomyces cerevisiae, a simpler scaffold consisting of γ-tubulin and GCP2-3 bestows its microtubule nucleating function. Although most microtubules in interphase cells are nucleated at the centrosome, this process relies on only a small fraction of the total soluble γ-tubulin that becomes recruited and activated there. A number of accessory proteins have been identified to be involved in the recruitment, stabilization and activation of the γ-TuRC presumably at the right time and subcellular region of the centrosome. Though, function of the γ-TuRC was attributed to microtubule nucleation by the pericentriolar material of the centrosome, very recent studies have uncovered its localization inside centrioles. Within centrioles, γ-TuRC interacts with the eight-subunit augmin complex. Its localization to the inner centriole suggests that γ-TuRC and augmin possess functions beyond microtubule nucleation. Moreover, the levels and organization of γ-TuRC differ markedly between fully mature and growing centrioles, indicating cell cycle–dependent recruitment and functional reprogramming during centriole biogenesis. Finally, we discuss how mutations in γ-TuRC genes impact development and are linked to cancer progression.