Cryo-EM shows mechanisms of polyubiquitination by cell-cycle regulator APC/C
Distinct cullin-RING-E2 architectures for multiubiquitination and chain elongation
RING activates UBE2C and binds substrate-linked ubiquitin to amplify processivity
RING delivers ubiquitin for K11-linked chain elongation by UBE2S placed by cullin