g-tubulin mainly localizes at centrosomes and play key roles in microtubule nucleation in eukaryotic cells. In many metazoans, g-tubulin forms two types of g-tubulin complexes, termed the g-tubulin small complex (gTuSC) and the g-tubulin ring complex (gTuRC), the latter of which consists of multiple gTuSCs and additional subunits. In C. elegans, the
tbg-1 gene encodes g-tubulin (Bobinnec et al., 2000; Strome et al., 2001; Hannak et al., 2002), and
gip-1 and
gip-2 encode the homologs of the components of gTuSC, Dgrip91/GCP3/Spc98p and Dgrip84/GCP2/Spc97p, respectively (Hannak et al., 2002). However, no clear homologs for the gTuRC-specfic components (Dgrip75/GCP4, Dgrip128/GCP5, Dgrip163/GCP6, and Dgrip71WD/GCP-WD) have been identified based on the sequence similarity, thus it is unclear whether a gTuRC-like complex is present in C. elegans. To clarify the composition of the g-tubulin complexes and their function in microtubule nucleation in C. elegans, we aimed to purify g-tubulin complexes from C. elegans embryos. We established integrant lines that express the FLAG-tagged TBG-1 protein and purified the TBG-1-associating proteins by immunoprecipitation. Mass spectrometric analysis revealed that GIP-1 and GIP-2 were included in the co-purified proteins, demonstrating that g-tubulin forms a complex with GIP-1 and GIP-2 in vivo, possibly as gTuSC. We are currently analyzing other proteins co-purified with TBG-1, and will ask whether or not a gTuRC-like complex exists in C. elegans.