Effect of KPC2 mutants on p27 ubiquitylation in vitro. Recombinant complexes of KPC1 and KPC2 derivatives were assayed for their abilities to mediate polyubiquitylation of p27 in the presence of Uba1, UbcH5A, GST-ubiquitin, and ATP. Reaction products were subjected to immunoblot (IB) analysis with antibodies to p27 or to GST (upper two panels). The bottom panels show immunoblot analysis of the amounts of recombinant KPC1 (tagged with the FLAG epitope) and KPC2 derivatives (tagged with the HA epitope) used in the reactions. WT, wild type; GST-Ub, GST-ubiquitin.