Fig. 6. The Mek1-dependent meiotic recombination checkpoint regulates phosphorylation of Cdc2 on Tyr15. (A) Meiotic time courses of wild-type (S964), meu13 (S1295) and meu13 mek1 (S1296) strains. The percentage of cells that have undergone the first meiotic division (2 nuclei) or both meiotic divisions (3/4 nuclei) is shown. Note that the meu13 mutant shows a delay (30 minutes) in entering meiosis I that is alleviated by the mek1 mutation. Arrows pointing to the percentage of binucleate cells at the 4 hour time point are shown to highlight the meu13 delay. (B) Western blot analysis of the meiotic time courses shown in A, also including a mek1 strain (S1293; see Fig. 4A), using anti-phopho-Cdc2(Tyr15) and anti-Cdc2 antibodies. Note that phosphorylation of Cdc2 on Tyr15 persists longer when the meiotic recombination checkpoint is triggered (i.e., in the meu13 mutant) but not when the checkpoint is inactivated by mutation of mek1⁺.