E3 ubiquitin-protein ligase which ubiquitinates itself in cooperation with an E2 enzyme UBE2D2/UBC4 and serves as a targeting signal for proteasomal degradation. May play a role in regulation of neuronal functions and may also participate in the formation or breakdown of abnormal inclusions in neurodegenerative disorders. May act as a regulator of synaptic vesicle exocytosis by controlling the availability of SNAP25 for the SNARE complex formation. 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 SNAP25. Enriched at synaptic terminals where it exists in a soluble form and a synaptic vesicle-associated form. Associated with the cytoskeleton (By similarity). Found in proximal dendrites of pyramidal neurons in the cerebral cortex and hippocampus, and Purkinje cells in the cerebellum (PubMed:20085810). Brain. Highly expressed in the cerebral cortex (at protein level). Severely decreased in the affected brain areas in Parkinson disease and dementia with Lewy bodies. The coiled coil domain mediates the interaction with the N-terminal t-SNARE domain of SNAP25. Auto-ubiquitinated. Poly-ubiquitinated in cultured cells, whereas it is monoubiquitinated in vitro. May be due to a competing donor splice site, to exon inclusion and to intron retention. May be due to intron retention. Belongs to the TRIM/RBCC family. Extended N-terminus.