Given these observations, we wondered whether the microtubule cytoskeleton has a function during the life Vaccinia virus infection disrupts microtubule organization and centrosome function The EMBO Journal Vol. 19 No. 15 pp. 3932±3944, 2000 cycle of vaccinia virus. We now report that the microtubule cytoskeleton and the dynein±dynactin complex play an important role during the early stages of vaccinia infection. However, later during the infection cycle, loss of centrosome function and accumulation of viral-encoded microtubule-associated proteins (MAPs) result in a dramatic rearrangement of the microtubule cytoskeleton.