Tubulin ( + ) in molecular biology can refer either to the tubulin protein superfamily of globular proteins, or one of the member proteins of that superfamily. a- and ß-tubulins polymerize into microtubules, a major component of the eukaryotic cytoskeleton.   Microtubules function in many essential cellular processes, including mitosis. Tubulin-binding drugs kill cancerous cells by inhibiting microtubule dynamics, which are required for DNA segregation and therefore cell division.