Fig. 7. Purification and ubiquitylation activity of APCΔdoc1. (A) Silver-stained SDS–PAGE analysis of APC purifications from CDC16-TAP (wild-type) and CDC16-TAP Δdoc1 yeast strains. An arrow indicates the position of the deleted Doc1p subunit. M = molecular weight markers. (B and C) Ubiquitylation activity of APCΔdoc1 with the substrates (B) [35S]Clb2, [35S]His6-Hsl1667–872 and (C) [35S]Pds1p. Doc1p produced in IVT or Doc1p purified from E.coli was added where indicated. The lower Hsl1 band is most probably an internal initiation product that does not contain the N-terminal tag.