Catalyzes the covalent attachment of ubiquitin to other proteins (PubMed:22496338). May be involved in hormonal homeostasis in females. Involved in regulation of B4GALT1 cell surface expression, B4GALT1-mediated cell adhesion to laminin and embryoid body formation (By similarity). 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. Monomer and homodimer. Only the homodimer is linked to ubiquitin through thiolester activation. Interacts (via N-terminus) with B4GALT1 (via N-terminal cytoplasmic domain). The interaction is direct. Widely expressed. Autoubiquitinated in vitro in the presence of NEDD4L. Belongs to the ubiquitin-conjugating enzyme family.