Fig. 2. The area occupied by -tubulin at prometaphase spindle poles is dependent on polymerized microtubules. CV-1 cells were treated for 30 minutes with either nocodazole added as a stock solution dissolved in DMSO (20 µM nocodazole, 0.1% DMSO final concentration) or with 0.1% DMSO only. Cells were fixed and stained with an anti--tubulin monoclonal antibody. Prometaphase cells were identified by morphology of DAPI-stained chromosomes and the area of increased -tubulin staining intensity was determined as described in Materials and Methods. The histogram shows the fraction of cells with -tubulin areas falling within each range of values shown.