Ubiquitin conjugating Enzyme H5c (UbcH5c), also known as Ubiquitinconjugating Enzyme E2D3 (UBE2D3), is a member of the yeast Ubc4/5 family of Ubiquitin conjugating (E2) enzymes. Human UbcH5c/UBE2D3 has a predicted molecular weight of 17 kDa and shares 88% and 89% amino acid sequence identity with the related family members, UbcH5a and UbcH5b, respectively. In combination with Ubiquitin ligases (E3s) such as CHIP, UbcH5c/UBE2D3 mediates the ubiquitination and subsequent degradation of several regulatory proteins . For instance, UbcH5c/UBE2D3 is involved in the polyubiquitination and proteasomemediated degradation of the Nuclear Factor kappaB (NFkappaB) inhibitor, IkappaBalpha, and is implicated in NFkappaBdependent inflammation. UbcH5c/UBE2D3 also mediates the ubiquitination of Histone H2A and PCNA, suggesting that it functions during transcriptional regulation, DNA replication, and DNA damage responses .