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Background
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Accepts ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins. Catalyzes monoubiquitination. Involved in degradation of misfolded chaperone substrates by mediating monoubiquitination of STUB1/CHIP, leading to recruitment of ATXN3 to monoubiquitinated STUB1/CHIP, and restriction of the length of ubiquitin chain attached to STUB1/CHIP substrates by ATXN3. After UV irradiation, but not after mitomycin-C (MMC) treatment, acts as a specific E2 ubiquitin-conjugating enzyme for the Fanconi anemia complex by associating with E3 ubiquitin-protein ligase FANCL and catalyzing monoubiquitination of FANCD2, a key step in the DNA damage pathway. In vitro catalyzes 'Lys-11'-linked polyubiquitination. Transfers ubiquitin in complex with RING/U-box type E3s that do not have active site cysteine residues to form thioester bonds with ubiquitin, and preferentially ubiquitinates the N-terminus of substrates, such as ATXN3, STUB1 and SUMO2.
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