Accepts ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins. In vitro catalyzes 'Lys-11'- and 'Lys-48'-, as well as 'Lys-63'-linked polyubiquitination (By similarity). Participates in the regulation of transepithelial sodium transport in renal cells. May be involved in cell growth arrest. S-ubiquitinyl-[E1 ubiquitin-activating enzyme]-L-cysteine + [E2 ubiquitin-conjugating enzyme]-L-cysteine = [E1 ubiquitin-activating enzyme]-L-cysteine + S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine. Protein modification; protein ubiquitination. Interacts with NEDD4L. The ubiquitin-loaded form interacts specifically with importin-11 (IPO11), leading to its import into the nucleus. Shuttles between the nucleus and cytoplasm in a IPO11-dependent manner. Belongs to the ubiquitin-conjugating enzyme family.