The well-organized microtubule cytoskeleton is essential for intracellular processes including cargo transport and mitotic spindle formation. The principal microtubule nucleator γ-tubulin ring complex (γTuRC) plays a vital role in spatial and temporal organization of microtubules at centrosomes and Golgi apparatus which are known as primary microtubule-organizing centers (MTOCs) in animal cells. GCP6 is the major component of γTuRC and is the longest one among all GCP components. However, we know little about how GCP6 is incorporated into γTuRC and what function GCP6 performs in γTuRC except for construction need. Here, by co-immunoprecipitation, I found that the unique N-terminal and middle regions of GCP6 are the MOZART1 and NME7 binding sites, respectively. However, the effect...[ Read more ]

The well-organized microtubule cytoskeleton is essential for intracellular processes including cargo transport and mitotic spindle formation. The principal microtubule nucleator γ-tubulin ring complex (γTuRC) plays a vital role in spatial and temporal organization of microtubules at centrosomes and Golgi apparatus which are known as primary microtubule-organizing centers (MTOCs) in animal cells. GCP6 is the major component of γTuRC and is the longest one among all GCP components. However, we know little about how GCP6 is incorporated into γTuRC and what function GCP6 performs in γTuRC except for construction need. Here, by co-immunoprecipitation, I found that the unique N-terminal and middle regions of GCP6 are the MOZART1 and NME7 binding sites, respectively. However, the effect of these two unique regions to GCP6 integrating into γTuRC is not related to MOZART1 and NME7. Furthermore, the GCP4, GCP5 and GCP6 can stay in a sub-complex conformation under both artificial high salt condition and in vivo. This suggests that GCP4-6 may first form a sub-complex in the γTuRC assembly process. The microtubule regrowth assay also shows that overexpression of GCP6 can inhibit centrosome-based microtubule nucleation. By contrast, the internal repeats have no effect on GCP6 incorporating into γTuRC and deletion of them can eliminate partial inhibition function of GCP6. Based on these results, for the first time I characterized the profiles of GCP6 unique regions. I proposed potential mechanisms of γTuRC assembly process and γTuRC activity regulation at centrosomes to provide new insights on the control of microtubule organization.