Microtubules perform essential and diverse functions in eukaryotic cells. They are required for spindles during mitosis and meiosis, for axonal transport, for organelle positioning, and for cilia and flagella. gamma-tubulin is necessary to initiate the assembly of alpha-beta tubulin heterodimers into microtubule polymers. Recent genetic analyses and database searches have added four new members of the tubulin superfamily, which now includes alpha-, beta-, gamma-, delta-, epsilon-, zeta-, and eta-tubulin.