Alternative titles; symbols
HGNC Approved Gene Symbol: TUBGCP3
Cytogenetic location: 13q34 Genomic coordinates (GRCh38): 13:112,485,011-112,605,630 (from NCBI)
The gamma-tubulin (TUBG; see 605785) ring complex is a microtubule-organizing center that acts as a template for polarized growth of microtubules essential for diverse cellular structures. The TUBG small complex, a component of the ring complex, consists of multimers of TUBGCP3, TUBGCP2 (617817), and TUBG and is the immediate template for growing microtubule ends (Riehlman et al., 2013).
By searching an EST database for sequences similar to yeast Spc98, followed by PCR of a HeLa cell cDNA library, Murphy et al. (1998) cloned TUBGCP3, which they called GCP3. GCP3 has 5 domains that are conserved with human GCP2 (TUBGCP2) and their respective yeast orthologs, Spc98 and Spc97. GCP3 has a predicted molecular mass of 104 kD. Immunohistochemical analysis showed colocalization of GCP2 and GCP3 with TUBG at centrosomes. Following expression in insect cells, GCP2 and GCP3 ran as a tight doublet at an apparent molecular mass of approximately 100 kD. Database analysis detected orthologs of GCP3 in mouse, zebrafish, and rice.
By EST database analysis, Tassin et al. (1998) identified 2 variants of SPC98 with different 3-prime ends. The deduced full-length 907-amino acid protein has a calculated molecular mass of 103.7 kD. The splice variant encodes a deduced 824-amino acid protein with a calculated molecular mass of 94 kD. The short isoform is identical to the full-length form over its N-terminal 816 residues. Northern blot analysis showed abundant expression of a 4.4-kb SPC98 transcript in all human tissues examined. Western blot analysis of KE37 human lymphoblastic cells detected SPC98 at an apparent molecular mass of 103 kD. SPC98 was enriched in the centrosomal fraction, but it was also detected in Triton X-100-soluble and -insoluble fractions. Immunohistochemical analysis of HeLa cells showed centrosomal SPC98 localization, and expression increased at the G2/M transition concomitant with elevated microtubule nucleation activity. SPC98 also localized to polar microtubules during metaphase and to midbody during anaphase. Immunoelectron microscopy revealed SPC98 within the pericentriolar material close to the centriole wall and at the tip of subdistal appendages surrounding the mother centriole. In Xenopus sperm cells, Spc98 localized to the inactive centrosome.
By coimmunoprecipitation analysis, Murphy et al. (1998) found that epitope-tagged human TUBG interacted with endogenous Gcp2 and Gcp3 in mouse 3T3 embryonic fibroblasts. Sucrose gradient fractionation of human 293 cells detected GCP2 and GCP3 in the same fraction with TUBG. The complex had a sedimentation coefficient of 32S. Both GCP2 and GCP3 sedimented with stabilized microtubules, and depolymerization of microtubules had no effect on association of GCP2 with GCP3 and TUBG. Epitope-tagged GCP3 colocalized with endogenous mouse Gcp3, in addition to Gcp2 and Tubg, suggesting that there are multiple copies of GCP3 in TUBG complexes.
By immunoprecipitation analysis, Tassin et al. (1998) found that HeLa cell SPC98 interacted with TUBG. The immunoprecipitate also contained TUBG ring complex proteins. A lower amount of SPC98 associated with alpha-tubulin (see 191110) protein complexes. Affinity-purified human SPC98 nucleated microtubule asters in an in vitro nucleation assay with isolated human centrosomes. In HeLa cells, antibody-mediated knockdown of SPC98 inhibited microtubule regrowth following depolymerization. Tassin et al. (1998) concluded that SPC98 is involved in growth of microtubules from centrosomes.
Riehlman et al. (2013) found that human GCP3, but not GCP2, assembled normally into a fission yeast Tubg ring complex of over 2 MDa. GCP3 replaced yeast Alp6 (Spc98) in the complex and rescued growth in yeast expressing a fatal Alp6 mutant. In contrast, GCP2 predominantly assembled into smaller Tubg complex and was unable to rescue yeast expressing defective Alp4 (Spc97).
By genomic sequence analysis, Murphy et al. (1998) mapped the TUBGCP3 gene to chromosome 13q34.
Hartz, P. A. Personal Communication. Baltimore, Md. 12/18/2017.
Murphy, S. M., Urbani, L., Stearns, T. The mammalian gamma-tubulin complex contains homologues of the yeast spindle pole body components Spc97p and Spc98p. J. Cell Biol. 141: 663-674, 1998. [PubMed: 9566967] [Full Text: https://doi.org/10.1083/jcb.141.3.663]
Riehlman, T. D., Olmsted, Z. T., Branca, C. N., Winnie, A. M., Seo, L., Cruz, L. O., Paluh, J. L. Functional replacement of fission yeast gamma-tubulin small complex proteins Alp4 and Alp6 by human GCP2 and GCP3. J. Cell Sci. 126: 4406-4413, 2013. [PubMed: 23886939] [Full Text: https://doi.org/10.1242/jcs.128173]
Tassin, A.-M., Celati, C., Moudjou, M., Bornens, M. Characterization of the human homologue of the yeast Spc98p and its association with gamma-tubulin. J. Cell Biol. 141: 689-701, 1998. [PubMed: 9566969] [Full Text: https://doi.org/10.1083/jcb.141.3.689]