Ubiquitin-conjugating enzymes, also known as UBE2W, E2 enzymes and more rarely as ubiquitin-carrier enzymes, perform the second step of protein ubiquitination. The modification of protein with ubiquitin is an important cellular mechanism for targeting abnormal or short-lived proteins for degradation. Ubiquitination involves at least three classes of enzymes: ubiquitin-activating enzymes, or E1s, ubiquitin-conjugating enzymes, or E2s, and ubiquitin-protein ligases, or E3s. UBE2W is a member of the E2 ubiquitin-conjugating enzyme family. This enzyme is required for post-replicative DNA damage repair. It accepts ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins. It also catalyzes monoubiquitination and "Lys-11"-linked polyubiquitination. UBE2W is also considered to regulate FANCD2 monoubiquitination. UBE2W exhibits ubiquitin conjugating enzyme activity and catalyzes the monoubiquitination of PHD domain of Fanconi anemia complementation group L (FANCL). Over-expression of UBE2W in cells promotes the monoubiquitination of FANCD2 and down-regulated UBE2W markedly reduces the UV irradiation-induced but not MMC-induced FANCD2 monoubiquitination.