They are composed of tightly bound dimers of a and b tubulin. These dimers will assemble into profilaments that will gather into groups of thirteen that form a tube of tubulins. It consists of two assemblies of microtubule triplets at right angles to each other. Colchicine and taxol, plant-derived toxins, both work by inhibiting microtubule function. Colchicine at low concentrations can block depolymerization and at high concentrations can induce depolymerization.
Temperature can also affect polymerization dramatically.
At 4'C, microtubules depolymerize and at 37'C microtubules repolymerize. The Golgi and ER are intimately associated with microtubules and reorganize themselves according to microtubule and MTOC 'directions'. It punches holes in the membrane of its victim by expelling vesicles of perforin into the space between the cells. These vesicles are made in the Golgi and must somehow find the right place to be released. Vesicles travel from the Golgi to the site of contact, where they will release their contacts.