E3 ubiquitin-protein ligase that acts in the endoplasmic reticulum (ER)-associated degradation (ERAD) pathway, which targets misfolded proteins that accumulate in the endoplasmic reticulum (ER) for ubiquitination and subsequent proteasome-mediated degradation. Protects cells from ER stress-induced apoptosis. 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. Expressed at highest levels in testis, lower levels in heart, liver, lung, and kidney (PubMed:17074343). Not detected in brain, ovary, and uterus (PubMed:17074343). Down-regulated in testis from patients with maturation arrest (MA) or Sertoli cell-only syndrome (SCOS) (PubMed:17074343). Ubiquitously expressed with high expression in testis (PubMed:27485036). Up-regulated by endoplasmic reticulum (ER) stress triggered by thapsigargin or tunicamycin. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay.