In vivo analysis of the functions of γ-tubulin-complex proteins

Abstract

To enhance our understanding of the function(s) of γ-tubulin-complex proteins (GCPs), we identified and analyzed the functions of the Aspergillus nidulans homologs of GCP2-GCP6 (here designated GCPB-GCBF). The γ-tubulin small complex (γ-TuSC) components, γ-tubulin, GCPB and GCPC, are essential for viability and mitotic spindle formation, whereas GCPD-GCPF are not essential for viability, spindle formation or sexual reproduction. GCPD-GCPF function in reducing the frequency of chromosome mis-segregation and in the assembly of large γ-tubulin complexes. Deletion of any of the γ-TuSC components eliminates the localization of all GCPs to the spindle pole body (SPB), whereas deletion of GCPD-GCPF does not affect localization of γ-TuSC components. Thus, GCPD-GCPF do not tether the γ-TuSC to the SPB, but, rather, the γ-TuSC tethers them to the SPB. GCPD-GCPF exhibit a hierarchy of localization to the SPB. Deletion of GCPF eliminates GCPD-GCPE localization to the SPB, and deletion of GCPD eliminates GCPE (but not GCPF) localization. All GCPs localize normally in a GCPE deletion. We propose a model for the structure of the γ-tubulin complex and its attachment to polar microtubule organizing centers.