Catalyzes the covalent attachment of ubiquitin to other proteins (Potential). Required for the maintenance of neuromuscular function (PubMed:12763049). 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. In the embryo, expressed in precursor neuron and muscle cells and in other cells such as hypodermal cells. After hatching of L1 larvae and in all subsequent stages, strongest expression in pharyngeal muscle and anal muscle cells. In L4 larvae and adolescent hermaphrodites, also expressed in the vulval muscles. Expression also detected in all four nerve cords and in neurons with weaker levels in all body wall muscles. Expression begins during gastrulation and continues during all subsequent stages. In males and hermaphrodites, late-onset paralysis of muscular functions required for locomotion and defecation. In addition, hermaphrodites show a progressive egg-laying defect, resulting in intrauterine hatching and premature death. Vulva protrusion is often observed with occasional rupture resulting in the projection of internal organs. Belongs to the ubiquitin-conjugating enzyme family.