Fig. 8. Model for the role of C. albicans Bub2p in regulating nuclear position. (A) In unperturbed wild-type cells, the bipolar spindle (yellow bar) migrates to the bud neck (orange) and elongates across the bud neck. After the dSPB/daughter nucleus (blue) resides in the bud, the spindle disassembles (dashed yellow line) and septation ensues (red). (B) Yeast cells lacking dynein-dynactin function undergo anaphase within the mother cell. Bub2p inhibits spindle disassembly and septation until the dSPB/daughter nucleus has moved into the bud. (C) Bub2p inhibits onset of anaphase and stimulates polarized growth in dyn1/ cells. In pseudohyphal-like cells lacking dynein, the bipolar spindle migrates into the elongating bud in a dynein-independent, bud length-dependent, fashion that might be mediated by interactions between the spindle and the bud tip. Spindle elongation eventually ensues. Spindle disassembly is not inhibited because the dSPB is already within the bud. Septation can occur before the mSPB/mother nucleus returns to the mother cell because no checkpoint is activated.