FIG. 3.

The rad50S mutant is proficient for linear element formation, whereas LEs are absent in the rad50Δ mutant. (a) Electron micrographs of lysed and spread meiotic nuclei. LEs in pat1-114 meiosis (used for its high degree of synchrony) were shorter than those in the WT (pat1⁺) (4), whereas networks and bundles were not detected. LEs in pat1-114 meiosis were classified into classes 1a (short LEs) and 1b (long LEs). LEs in rad50S cells were slightly longer and more abundant than those in the WT. LEs were absent in rad50Δ cells. The bottom two panels (rad50Δ) illustrate typical SPB orientations in mitotic (opposite the nucleolus [NLL]) and meiotic (next to the nucleolus) cells. This allows the distinction between mitotic and meiotic cells and confirms that rad50Δ cells underwent meiosis in the absence of LEs. (b) (Left top and middle) Quantification of LE classes 1a and 1b at different time points. Class 1b was more abundant in rad50S cells than in the WT. (Bottom left) Quantification of rad50Δ cells (without LEs) containing an SPB configuration indicative of meiosis. At later time points, cells started to form ascus and spore walls, making the cells resistant to lysis, which led to an artifactual underrepresentation of meiotic cells. (Right) Quantification of DAPI (4′,6-diamidino-2-phenylindole)-visualized elongated (horsetail) nuclei indicative of meiotic prophase. The percentage of cells with more than one nucleus indicates progression through the first and second meiotic divisions. All quantifications are based on at least 100 cells per time point.