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 (By similarity). 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 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 (By similarity). Interacts with RARB. A significant portion localizes to the endoplasmic reticulum. Targeted to Golgi membrane via its interaction with Rab proteins (By similarity). Mice develop spontaneous, late-onset cancer. Moreover, tumor incidence in mice heterozygous for a p53/Tp53 mutation in higher in a Hace1-deficient background. Extended N-terminus.