E3 ubiquitin-protein ligase involved in Golgi membrane fusion and regulation of small GTPases. Acts as a regulator of Golgi membrane dynamics during the cell cycle: recruited to Golgi membrane by Rab proteins and regulates postmitotic Golgi membrane fusion. Acts by mediating ubiquitination during mitotic Golgi disassembly, ubiquitination serving as a signal for Golgi reassembly later, after cell division. Specifically interacts with GTP-bound RAC1, mediating ubiquitination and subsequent degradation of active RAC1, thereby playing a role in host defense against pathogens. May also act as a transcription regulator via its interaction with RARB. 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 RARB (By similarity). Interacts with RAB1 (RAB1A, RAB1B or RAB1C), RAB4 (RAB4A or RAB4B) and RAB11 (RAB11A or RAB11B); in a GTP-dependent manner. Interacts with RAC1; in a GTP-dependent manner. Interacts with the 26S proteasomal complex through the 20S core proteasomal subunit. A significant portion localizes to the endoplasmic reticulum. Targeted to Golgi membrane via its interaction with Rab proteins. Expressed in multiple tissues including heart, brain and kidney. Expressed in fetal and pediatric kidney cells. Down-regulated in sporadic Wilms tumor. Defects in HACE1 are a cause of Wilms tumor (WT). WT is a pediatric malignancy of kidney and one of the most common solid cancers in childhood. HACE1 is epigenetically down-regulated in sporadic Wilms tumor. Moreover, a t(5;6)(q21;q21) translocation that truncates HACE1 has been found in a child with bilateral, young-onset Wilms tumor (PubMed:19948536). The disease is caused by variants affecting the gene represented in this entry. Extended N-terminus. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus.