FIGURE 3.

Preanaphase spindle assembly is mistimed in the DIS3, MTR3, and MTR4 mutants. (A) Schematic showing the coordination among nuclear migration, bud formation, and spindle formation, orientation, alignment, and disassembly in a normal cell cycle of Saccharomyces cerevisiae. The roman numerals signify the arbitrary stages. Note that the preanaphase spindle forms in stage IV, when the bud has almost achieved its full size. Adapted from (Shaw et al. 1997). (B) Preanaphase spindles are displaced from the bud neck in mtr mutants. In this analysis, the positioning of the spindle and the nucleus (DNA stain) was scored relative to the bud neck. There is a strong correlation between preanaphase spindle misorientation and mispositioning. (C) mtr mutants uncouple normal spindle assembly timing from bud growth. These mutants have a preanaphase spindle (observed in stage IV) in a cell that morphologically is at stage II or III. This phenotype is observed both at the permissive and restrictive temperature (right panel).