Background of the antigen
MARCH4, an E3 ubiquitin protein ligase, may mediate ubiquitination of MHC I and CD4, and promote their subsequent endocytosis and sorting to lysosomes via multivesicular bodies. E3 ubiquitin protein ligases accept ubiquitin from an E2 ubiquitin conjugating enzyme in the form of a thioester and then directly transfer the ubiquitin to targeted substrates.