The RING domain of E3 ubiquitin transferase serves as a mediator bringing the ubiquitin-charged E2 ubiquitin-conjugating enzyme and the acceptor protein together to enable the direct transfer of ubiquitin through the formation of an isopeptide bond between the C-terminal glycine residue of ubiquitin an the epsilon-amino group of an L-lysine residue of the acceptor protein. The RING-E3 domain does not form a catalytic thioester intermediate with ubiquitin (unlike the HECT domain, EC 220.127.116.11). RING-type ubiquitin transferases may occur as single-chain enzymes but also in dimeric forms or in multi-subunit assemblies.
isoform RNF220 specifically interacts with Sin3B both in vitro and in vivo. Sin3B can be regulated by the ubiquitin-proteasome system. Co-expression of RNF220 and Sin3B promotes the ubiquitination and proteasomal degradation of Sin3B