Fig. 6. Securin has two conserved sequences that signal its APC/C-specific degradation. Cells stably expressing securin-DM–CAT (filled circles), which carries a mutated d-box, securin-KAA–CAT (filled squares) with a mutated KEN box and securin-KAA-DM–CAT (open squares) with a double mutation were generated. These cells were released from a nocodazole block, harvested at the indicated time points and the CAT assays are shown in the top panels. The quantified CAT activity of the above mutants, as well as of wild-type securin–CAT (open circles), shown in Figure 3, is plotted in the bottom panel.