This is the N-terminal domain found in components of the gamma-tubulin complex proteins (GCPs). Family members include spindle pole body (SBP) components such as Spc97 and Spc98 which function as the microtubule-organizing center in yeast [1]. Furthermore, family members such as human GCP4 (Gamma-tubulin complex component 4) have been structurally elucidated Swiss:Q9UGJ1 [2]. Functional studies have shown that the N-terminal domain defines the functional identity of GCPs, suggesting that all GCPs are incorporated into the helix of gamma-tubulin small complexes (gTURCs) via lateral interactions between their N-terminal domains. Thereby, they define the direct neighbors and position the GCPs within the helical wall of gTuRC [3]. Sequence alignment of human GCPs based on the GCP4 structure helped delineate conserved regions in the N- and C-terminal domains [2]. In addition to the conserved sequences, the N-terminal domains carry specific insertions of various sizes depending on the GCP, i.e. internal insertions or N-terminal extensions. These insertions may equally contribute to the function of individual GCPs as they have been implied in specific interactions with regulatory or structural proteins. For instance, GCP6 carries a large internal insertion phosphorylated by Plk4 and containing a domain of interaction with keratins, whereas the N-terminal extension of GCP3 interacts with the recruitment protein MOZART1[3].

1: Characterization and reconstitution of Drosophila gamma-tubulin ring complex subunits. Gunawardane RN, Martin OC, Cao K, Zhang L, Dej K, Iwamatsu A, Zheng Y; J Cell Biol. 2000;151:1513-1524. PMID:11134079

2: Crystal structure of gamma-tubulin complex protein GCP4 provides insight into microtubule nucleation. Guillet V, Knibiehler M, Gregory-Pauron L, Remy MH, Chemin C, Raynaud-Messina B, Bon C, Kollman JM, Agard DA, Merdes A, Mourey L; Nat Struct Mol Biol. 2011;18:915-919. PMID:21725292

3: Functional Analysis of gamma-Tubulin Complex Proteins Indicates Specific Lateral Association via Their N-terminal Domains. Farache D, Jauneau A, Chemin C, Chartrain M, Remy MH, Merdes A, Haren L; J Biol Chem. 2016;291:23112-23125. PMID:27660388