Figure 3.

Illustration of the changes in chromatin condensation during meiotic time courses in wild-type and top2 cells at 34°C. Quantitative data on these time courses are presented in Figure 2. At 0 h the majority of the still mitotic cells are in G₂ (also see Figure 2A) and show a dense nuclear staining. At 2 h the cells have performed a mitotic division (see Figure 2E), are smaller, and have a lower DNA content. The nuclei are densely stained, and the level of chromatin condensation is similar to that at 0 h (see Figure 2D). At 3 h the cells still have a DNA content similar to 0 h but are larger because of chromatin decondensation (see Figure 2D) and show a more open chromatin structure. At 4 h the cells have recondensed again, showing the dense nuclear staining. At 8 h nuclei are visible, which show the typical prophase nuclear morphology (horse tail nuclei). During this time DNA replication takes place. In wild type at 11 h, shortly before the first meiotic division, the nuclei condense again, showing a dense nuclear staining. In the top2 mutant at 11 h the cells do not condense and show a more open chromatin structure. Bar, 10 μm.