ABSTRACT
This chapter introduces the protein tubulin and examines how it assembles into microtubules. Nucleotide hydrolysis and conformational changes make the assembly of tubulin into polymer a sensitive, hesitant process responsive to its surroundings and easily switched from net growth to net disassembly. The protein they isolated, known as tubulin, was later shown to reassemble into microtubules under defined conditions. Like actin, myosin, tropomyosin, and many other cytoskeletal proteins, tubulin is produced by a family of closely related genes. Cells treated with taxol develop large aggregates of microtubules in their cytoplasm, an effect that inhibits many cellular processes as surely as microtubule depolymerization. Microtubules need nucleating sites such as those provided by the γ-tubulin rings in the centrosome. Microtubule-associated proteins have important, although often subtle, effects on the dynamic properties of microtubules. Differentiated cells of many kinds contain highly stable microtubules that fail to be solubilized, and are consequently discarded, during conventional biochemical extractions.
