A, B Schematic of UBE2S~Ub (A) and UBE2C~Ub interactions (B) with the APC/C. UBE2S~Ub uses its C-terminal extension to bind to a groove formed by APC2 and APC4. The UBE2SHTH interacts with APC2 and the APC11 RING domain positions the substrate-linked Ub for chain elongation. UBE2C~Ub is positioned by the APC11RING and APC2 winged-helix B (WHB) domains during substrate ubiquitination (Brown et al., 2015; Brown et al., 2016). 