C APC/C-UBE2S-dependent diUb synthesis was monitored by fluorescent scanning (left), quantitated (right), and assessed for statistical significance by two-way ANOVA (* p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001, **** p ≤ 0.0001, n=3 independent, technical replicates), demonstrating that the UBE2SHTH substitutions rescue the defects in diUb synthesis created by mutating APC2. Error bars: SEM. Data normalized to WT APC/C-UBE2S diUb reactions. D APC/C Platform-dependent activation of UBE2S-mediated diUb synthesis was monitored by fluorescent scanning (left), quantitated (right), and assessed for statistical significance by two-way ANOVA (* p ≤ 0.05, *** p ≤ 0.001, **** p ≤ 0.0001, n=3 independent, technical replicates). Error bars: SEM. Data normalized to WT APC/C Platform-UBE2S diUb reactions. 