Figure 6.

Microtubule penetration in the bud precedes nuclear movement to the neck. Montage from time-lapse experiments demonstrating that once cytoplasmic astral microtubules penetrate the bud, the nucleus migrates to the bud neck. Unbudded haploid cells (9dΔd containing pKBY701) were captured in the process of bud emergence. A series of DIC (right) and fluorescence (left) images over the time course indicated in the lower left (min) are shown from top to bottom, in consecutive series. In the upper left quadrant, the unbudded cell has a single SPB (embedded in the nuclear envelope), that is positioned at approximately five o'clock. In the next sequence, the SPB has migrated to approximately the seven o'clock position. Note that the astral microtubules trail the SPB and form a conical array. The position of bud emergence is six o'clock (see 47 min). The SPB migrates around the cell periphery until the 9–10 o'clock position (47 min), well past the emerging bud. At this time, a long microtubule (7 μm) can be seen extended toward and into the bud. The nucleus migrates in the direction of the bud after microtubule penetration of the bud (57–69 min). The nucleus continues toward the bud neck, in the direction of the microtubule over the next 23 min (69–92 min). Fluorescently labeled SPBs were apparent at 117 min. Bar, 2 μm.