Figure 4.

Meiotic time courses with the top2 mutant and the wild type (wt) at 24°C (permissive temperature) and 34°C (restrictive temperature). For details see MATERIALS AND METHODS. The delay in linear element formation in the top2 strain at 24°C (C) was within the normal variation between the different time courses. In the wild-type cells at 24°C (A, 13 h) and in the top2 cells at 34°C (D, 17 h) the percentage of linear element containing cells seemed to increase after a while. This was due to a spreading artifact, caused by selection against cells that were in late stages of meiosis and were not properly protoplasted. This led to an overrepresentation of early cells late in the time courses. In the top2 strain at 24°C (C) the meiotic divisions were delayed, possibly because the top2 mutant is not completely wild type at permissive temperature (also see Figure 1 legend). >1 nucleus, percentage of cells that performed the first meiotic division; Horse tail, percentage of cells that show a nuclear morphology typical of prophase after DAPI staining and fluorescence microscopy; l. elements, percentage of cells that contain linear elements (electron microscopy).