The function of UBE2W (ubiquitin conjugating enzyme E2 W, Ensembl gene identifier ENSG00000104343) is as follows. Accepts ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins (PubMed:20061386, PubMed:21229326). Specifically monoubiquitinates the N-terminus of various substrates, including ATXN3, MAPT/TAU, POLR2H/RPB8 and STUB1/CHIP, by recognizing backbone atoms of disordered N-termini (PubMed:23560854, PubMed:23696636, PubMed:25436519). 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 (PubMed:19111657, PubMed:21229326). In vitro catalyzes 'Lys-11'-linked polyubiquitination. UBE2W-catalyzed ubiquitination also occurs in the presence of inactive RING/U-box type E3s, i.e. lacking the active site cysteine residues to form thioester bonds with ubiquitin, or even in the absence of E3, albeit at a slower rate (PubMed:25436519). {ECO:0000269|PubMed:19111657, ECO:0000269|PubMed:20061386, ECO:0000269|PubMed:21229326, ECO:0000269|PubMed:23560854, ECO:0000269|PubMed:23696636, ECO:0000269|PubMed:25436519}.