The sudden recruitment of gamma-tubulin to the centrosome at the onset of mitosis and its dynamic exchange throughout the cell cycle, do not require microtubules

gamma-Tubulin is a centrosomal component involved in microtubule nucleation . To determine how this molecule behaves during the cell cycle, we have est ablished several vertebrate somatic cell lines that constitutively express a gamma-tubulin/green fluorescent protein fusion protein. Near simultaneous fluorescence and DIC light microscopy reveals that the amount of gamma-tub ulin associated with the centrosome remains relatively constant throughout interphase, suddenly increases during prophase, and then decreases to inter phase levels as the cell exits mitosis. This mitosis-specific recruitment o f gamma-tubulin does not require microtubules, Fluorescence recovery after photobleaching (FRAP) studies reveal that the centrosome possesses two popu lations of gamma-tubulin: one that turns over rapidly and another that is m ore tightly bound. The dynamic exchange of centrosome-associated gamma-tubu lin occurs throughout the cell cycle, including mitosis, and it does not re quire microtubules, These data are the first to characterize the dynamics o f centrosome-associated gamma-tubulin in vertebrate cells in vivo and to de monstrate the microtubule-independent nature of these dynamics, They reveal that the additional gamma-tubulin required for spindle formation does not accumulate progressively at the centrosome during interphase, Rather, at th e onset of mitosis, the centrosome suddenly gains the ability to bind great er than three times the amount of gamma-tubulin than during interphase.