CENTROSOMES AND MICROTUBULES - WEDDED WITH A RING

How centrosomes nucleate microtubule growth is a question that has puz zled cell biologists for decades. If has been suspected for some time that a centrosome contains multiple copies of a basic microtubule-nucl eating structure, each of which is responsible for nucleating a single microtubule. This suspicion has now been confirmed. A ring of gamma-t ubulin molecules, associated with a large protein complex, apparently serves as the long-sought-after microtubule-nucleating structure.