CDC5 is sufficient to inactivate Mek1. The CDC5-IN ndt80Δ diploid, NH2296, was transferred to Spo medium and incubated for 7 hr, at which time the culture was split in half and either DMSO (−ED) or a final concentration of 1 μM ED (+ED) was added. Protein extracts were then probed with antibodies against, Cdc5, Hop1, Mek1, phospho-Hed1 T40 (p-Hed1), Hed1, Red1, Zip1, and Rec8. Arp7 was used as a loading control. This experiment was repeated five times with similar results. ED, estradiol; Spo, sporulation medium.