Has no ubiquitin ligase activity on its own. The heterodimer with UBC catalyzes the synthesis of non-canonical poly-ubiquitin chains that are linked through 'Lys-63'. This type of poly-ubiquitination does not lead to protein degradation by the proteasome. Mediates transcriptional activation of target genes. May play a role in the control of progress through the cell cycle and differentiation. May play a role in the error-free DNA repair pathway and contributes to the survival of cells after DNA damage. Heterodimer with UBC35 or UBC36. A number of isoforms are produced. According to EST sequences. Expressed in roots, shoots, leaves, stems and flowers, but not in pollen. Not detected in seedlings 6 hours or 2 days post-germination. Not induced by stresses. Belongs to the ubiquitin-conjugating enzyme family.