Tubulin is a major cytoskeleton component that has five distinct forms, designated a, b, g, d and e tubulin. a and b tubulins form heterodimers which multimerize to form a microtubule filament. Multiple b Tubulin isoforms (b1, b2, b3, b4, b5, b6 and b8) have been characterized and are expressed in mammalian tissues. b1 and b4 are present throughout the cytosol, b2 is present in the nuclei and nucleoplasm, and b3 is a neuron-specific cytoskeletal protein. GammaTubulin forms the gammasome, which is required for nucleating microtubule filaments at the centrosome. Both d Tubulin and Delta Tubulin are associated with the centrosome. Gamma Tubulin is a homolog of the Chlamydomonas Gamma Tubulin Uni3 and is found in association with the centrioles, whereas e Tubulin localizes to the pericentriolar material. Delta Tubulin exhibits a cell cycle-specific pattern of localization; first associating with only the older of the centrosomes in a newly duplicated pair, and later associating with both centrosomes.