E3 ubiquitin-protein ligase which accepts ubiquitin specifically from endoplasmic reticulum-associated UBC7 E2 ligase and transfers it to substrates, promoting their degradation (PubMed:12975321, PubMed:15611074). Component of the endoplasmic reticulum quality control (ERQC) system also called ER-associated degradation (ERAD) involved in ubiquitin-dependent degradation of misfolded endoplasmic reticulum proteins (PubMed:12975321, PubMed:15611074). Also promotes the degradation of normal but naturally short-lived proteins such as SGK. Protects cells from ER stress-induced apoptosis. Sequesters p53/TP53 in the cytoplasm and promotes its degradation, thereby negatively regulating its biological function in transcription, cell cycle regulation and apoptosis (PubMed:17170702). Required for embryogenesis (PubMed:15611074). Mediates the ubiquitination and subsequent degradation of cytoplasmic NFE2L1 (PubMed:21911472). During the early stage of B cell development, required for degradation of the pre-B cell receptor (pre-BCR) complex, hence supporting further differentiation into mature B cells (PubMed:29907570). 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 (By similarity). Interacts with p53/TP53 (PubMed:17170702). Interacts with HTT (By similarity). Component of the HRD1 complex, which comprises at least SYNV1/HRD1, DERL1/2, FAM8A1, HERPUD1/HERP, OS9, SEL1L and UBE2J1 (PubMed:27064360) (By similarity). FAM8A1 is stabilized by interaction with SYNV1, which prevents its proteasomal degradation. OS9 and UBE2J1 recruitment to the complex may be mediated by SEL1L (By similarity). SYNV1 assembles with SEL1L and FAM8A1 through its transmembrane domains, but interaction with its cytoplasmic domain is required to confer stability to FAM8A1 and enhance recruitment of HERPUD1 (By similarity). The HRD1 complex also associates with VIMP and may transfer misfolded proteins from the endoplasmic reticulum to VCP (By similarity). May form a complex with ERLEC1; HSPA5; OS9 AND SEL1L (By similarity). Interacts with VCP (By similarity). Interacts with UBXN6 (By similarity). Interacts with BAG6 (By similarity). Interacts with NFE2L1 (PubMed:21911472). Interacts (via N-terminus) with components of the pre-B cell receptor, including IGLL1 and VPREB1 (PubMed:29907570). Interacts with CREB3L3; this interaction leads to CREB3L3 ubiquitination and proteasomal degradation (PubMed:30389664). Widely expressed, with highest levels in bone, spleen, lung and testis. In the brain, present in neurons but not in glial cells. Up-regulated in synovial tissues from mice with collagen-induced arthritis (at protein level). Expressed in the liver (PubMed:30389664). Up-regulated in conditions of cerebral ischemia (PubMed:15519674). In the liver, induced in postprandial conditions (PubMed:30389664). The RING-type zinc finger is required for E3 ligase activity. Auto-ubiquitinated. Mice overexpressing Syvn1 develop severe spontaneous arthropathy. Mice lacking Syvn1 die in utero around 13.5 dpc due to augmented apoptotic cell death. Belongs to the HRD1 family.