The cytoskeleton consists of three types of cytosolic fibers: microfilaments (actin filaments), intermediate filaments and microtubules. Globular tubulin subunits are the building blocks of a microtubule, and the alpha/beta tubulin heterodimer forms the tubulin subunit, which is present in all eukaryotic cells. gamma-tubulin is necessary to nucleate polymerization of tubulin subunits to form microtubules. Many cell movements, including beating of cilia and flagella, transport of membrane vesicles in the cytoplasm, alignment of chromosomes during meiosis and mitosis and migration of nerve-cell axons by extending the neuronal growth cone, are mediated by microtubules. These movements are either the result of polymerization and depolymerization or the actions of microtubule motor proteins (1).