 At the C-terminal end, CUL4A interacts with the RBX1/ROC1 protein via its RING domain.RBX1 is a core component of Cullin-RING ubiquitin ligase (CRL) complexes and functions to recruit E2 ubiquitin conjugating enzymes.Therefore, the C-terminus of CUL4A - along with RBX1 and activated E2 enzymes - compose the catalytic core of CRL4 complexes.