E3 ubiquitin ligase catalyzing the covalent attachment of ubiquitin moieties onto substrate proteins (PubMed:20657603). May operate on tyrosine-phosphorylated SRC substrates (PubMed:22252131). 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. Homodimer. Localized over the postacrosomal perinuclear theca region and the entire length of sperm tail. Exclusively expressed in testis and sperm, including spermatocytes, round and elongated spermatids, and Leydig cells. The HYB domain forms a phosphotyrosine-binding pocket upon dimerization, and mediates as well the recognition of its flanking acidic amino acids.