The ring saga: looking back at the discovery of ?-tubulin and ?-tubulin ring complexes

For many years, two central, unanswered questions in cytoskeleton research were how microtubule assembly is nucleated and microtubule polarity established. The dis-coveries of gamma-tubulin and gamma-tubulin ring complexes were key advances that allowed these questions to be substantially answered. The discovery of gamma-tubulin was the product of a ge-netic screen in Aspergillus nidulans for genes important for microtubule function. gamma-Tubulin is a member of the tubulin superfamily of proteins, closely related to alpha- and beta-tubulin but dis-tinct from both. It is ubiquitous in eukaryotes, and in many organisms there are small families of gamma-tubulin genes. gamma-Tubulin and associated proteins form ring-like complexes that localize to microtubule-organizing centers (MTOCs) and play an important role in the nucleation of mi-crotubule assembly from MTOCs and the establishment of microtubule polarity.