Probable E3 ubiquitin-protein ligase which plays an important role in blastocyst development. Involved in progression of blastocyst stage and subsequent embryo development. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Interacts with USP5. Testis. Expressed from two-cell to blastocyst stage of embryo development.