UBE2D3 (UbcH5b) is an E2 (ubiquitin conjugating enzyme) that is involved in the conjugation of ubiquitin to target substrates along with E1 and E3 enzymes. The UbcH5 family (including UbcH5a and UbcH5c, having 88% and 89% sequence identity with UbcH5b respectively) are the human homologues of the Saccharomyces cerevisiae UBC4/5 family (~79% sequence identity). Members of the UbcH5 family have been implicated in a number of inflammatory and cancer pathways including the ubiquitylation of p53 and IκBα with the help of different E3 ligases (Hdm2 and SCF complexes respectively).