Fig. 3. Ubiquitylation of substrates containing D and KEN box mutations. APC ubiquitylation assays were performed on ³⁵S-labelled (A) Pds1p and (B) Clb2p mutants. Pds1^dbm, Pds1^dkbm, Clb2^dbm and Clb2^dkbm contained D box mutations, and Pds1^kbm, Pds1^dkbm, Clb2^kbm and Clb2^dkbm contained KEN box mutations.