Accepts the ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins. Part of the anaphase-promoting complex (APC). May have a key function during cell cycle and be involved in cyclin B1 degradation. 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. Expressed in all tissues with cell division activities and in mature leaves. Expressed during the G1-S phases of the cell cycle. Not induced by heat shock, dark to light transition, proteasome inhibitor MG132 or geldanamycin. Belongs to the ubiquitin-conjugating enzyme family.