The budding yeastSaccharomyces cerevisiaehas become a laboratory favorite for the study of several microtubule-dependent processes, including assembly of the mitotic spindle and spindle positioning. This is owing not only to the pliancy of its genetic system but also to the simplicity of its microtubule structures, which can be viewed by indirect immunofluorescence.S. cerevisiaecontains two sets of microtubules, the intranuclear microtubules, which comprise the major element of the mitotic spindle, and the cytoplasmic (or astral) microtubules, which play an important role in positioning the mitotic spindle through interactions with the cortex (1 –5 ). In yeast, the spindle is assembled within the nucleus, as the nuclear envelope remains intact at all stages of the cell cycle (6 ). Cytoplasmic microtubules are attached to the nucleus at the yeast’s microtubule organizing center, or spindle-pole body (SPB), which is embedded in the nuclear envelope (7 ,8 ).
