Figure 6.

Expression of TUB1-828 after spindles have assembled disrupts spindle integrity and inhibits normal spindle elongation. Strain DBY9580, containing either pTS210 (GAL1p-vector), pRB2785 (GAL1p-TUB1), or pRB2949 (GAL1p-TUB1-828), was released from G1 α-factor arrest into medium containing hydroxyurea for 2.5 h. Galactose was added and the cells incubated for 2 h. Cells were then released from hydroxyurea-induced arrest into glucose medium at time zero. α-Factor was included to prevent a second cell division. (A) Cell cycle progression after release from hydroxyurea-induced arrest. Numbers of nuclei were determined by 4′,6′-diamidino-2-phenylindole staining and fluorescence microscopy. At least 100 cells were counted for each time point. (B) GFP-labeled microtubules 90–120 min after release from hydroxyurea. Arrows indicate thinning or disappearance of intranuclear microtubules that span the distance between spindle pole bodies; arrowheads indicate bundled cytoplasmic microtubules. Bar, 3 μm.