Component of the endoplasmic reticulum quality control (ERQC) system involved in ubiquitin-dependent degradation of misfolded endoplasmic reticulum proteins. Component of the HRD1 ubiquitin ligase complex, which is part of the ERAD-L and ERAD-M pathways responsible for the rapid degradation of soluble lumenal and membrane proteins with misfolded lumenal domains (ERAD-L), or ER-membrane proteins with misfolded transmembrane domains (ERAD-M). ERAD-L substrates are ubiquitinated through HRD1 in conjunction with the E2 ubiquitin-conjugating enzymes UBC1 and UBC7-CUE1. Ubiquitinated substrates are then removed to the cytosol via the action of the CDC48-NPL4-UFD1 ATPase complex and targeted to the proteasome. ERAD-M substrates are processed by the same HRD1-HRD3 core complex, but only a subset of the other components is required for ERAD-M. Stabilizes the HRD1 ubiquitin-protein ligase. Also functions in recruiting misfolded protein substrates in conjunction with YOS9. Component of the HRD1 ubiquitin ligase complex which contains the E3 ligase HRD1, its cofactors HRD3, USA1 and DER1, substrate recruiting factor YOS9 and CDC48-binding protein UBX2 (PubMed:16873065, PubMed:16873066, PubMed:16845381). Within the complex, interacts directly with HRD1 and YOS9 (via N-terminus) (PubMed:11018054, PubMed:22262864, PubMed:28682307). In ERAD-L, HRD3 and YOS9 jointly bind misfolded glycoproteins in the endoplasmic reticulum (ER) lumen (PubMed:32327568). Movement of ERAD-L substrates through the ER membrane is facilitated by HRD1 and DER1 which have lateral gates facing each other and which distort the membrane region between the lateral gates, making it much thinner than a normal phospholipid bilayer (PubMed:32327568). Substrates insert into the membrane as a hairpin loop with one strand interacting with DER1 and the other with HRD1 (PubMed:32327568). The HRD1 complex interacts with the heterotrimeric CDC48-NPL4-UFD1 ATPase complex which is recruited by UBX2 via its interaction with CDC48 and which moves ubiquitinated substrates to the cytosol for targeting to the proteasome (PubMed:16873066, PubMed:16619026). The HRD1 complex interacts with the ERAD substrates HMG1 and HMG2 (PubMed:11390656). Interacts with KAR2 (PubMed:16873065). Belongs to the sel-1 family.