Alternative products: Additional isoforms may exist. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay, function: Gamma-tubulin complex is necessary for microtubule nucleation at the centrosome. similarity: Belongs to the GCP family. subunit: Gamma-tubulin complex is composed of gamma-tubulin, GCP2, GCP3, GCP4, GCP5 and GCP6. tissue specificity: Ubiquitously expressed.