FUNCTION 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. Participates in the regulation of transepithelial sodium transport in renal cells.CATALYTIC ACTIVITY 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.PATHWAY Protein modification; protein ubiquitination.SUBUNIT The ubiquitin-loaded form interacts specifically with importin-11 (IPO11), leading to its import into the nucleus. Interacts with NEDD4L.INTERACTION Shuttles between the nucleus and cytoplasm in a IPO11-dependent manner.TISSUE SPECIFICITY Ubiquitously expressed at low levels. Highly expressed in skeletal muscle.SIMILARITY Belongs to the ubiquitin-conjugating enzyme family.