WHAT ARE TUBULINS? Tubulins are globular GTP-binding proteins. The tubulin superfamily contains six families of related proteins that arose from a single ancestral protein near to the emergence of the last eukaryotic common ancestor. α-, β-, and γ-tubulins are universal and essential in all eukaryotes. Microtubules, assembled from α-β-tubulin heterodimer subunits, underlie a variety of cellular processes, particularly mitosis and meiosis, but also motility, cell shape, and intracellular trafficking and γ-tubulins coordinate microtubule nucleation. The remaining tubulin families (δ-, ε-, ζ-) participate in construction of specialized microtubule structures and are not found in all eukaryotes. Tubulins are highly conserved due to functional constraints: they must maintain interactions with GTP, as well as with a multitude of proteins including other tubulins, motors and microtubule associated proteins. Phylogenetic analysis (Findeisen et al, 2014) locates unusual protozoan tubulins (eta, theta, iota, and kapa) as deep branching members of the α-tubulin (κ-), β-tubulin (θ, ι) or ζ-tubulin (η) families. We indexed these proteins using this information.