The function of ENSG00000127481 (UBR4, ubiquitin protein ligase E3 component n-recognin 4) is as follows. E3 ubiquitin-protein ligase involved in different protein quality control pathways in the cytoplasm (PubMed:25582440, PubMed:29033132, PubMed:34893540, PubMed:37891180, PubMed:38030679, PubMed:38182926, PubMed:38297121). Component of the N-end rule pathway: ubiquitinates proteins bearing specific N-terminal residues that are destabilizing according to the N-end rule, leading to their degradation (PubMed:34893540, PubMed:37891180, PubMed:38030679). Recognizes both type-1 and type-2 N-degrons, containing positively charged amino acids (Arg, Lys and His) and bulky and hydrophobic amino acids, respectively (PubMed:38030679). Does not ubiquitinate proteins that are acetylated at the N-terminus (PubMed:37891180). Together with UBR5, part of a cytoplasm protein quality control pathway that prevents protein aggregation by catalyzing assembly of heterotypic 'Lys-11'-/'Lys-48'- linked branched ubiquitin chains on aggregated proteins, leading to substrate recognition by the segregase p97/VCP and degradation by the proteasome: UBR4 probably synthesizes mixed chains containing multiple linkages, while UBR5 is likely branching multiple 'Lys-48'-linked chains of substrates initially modified (PubMed:29033132). Together with KCMF1, part of a protein quality control pathway that catalyzes ubiquitination and degradation of proteins that have been oxidized in response to reactive oxygen species (ROS): recognizes proteins with an Arg-CysO3(H) degron at the N-terminus, and mediates assembly of heterotypic 'Lys-63'-/'Lys-27'-linked branched ubiquitin chains on oxidized proteins, leading to their degradation by autophagy (PubMed:34893540). Catalytic component of the silencing factor of the integrated stress response (SIFI) complex, a multiprotein complex that turns off the mitochondrial stress response after a specific stress event has been resolved (PubMed:38297121, PubMed:40328314, PubMed:40875847). The SIFI complex ubiquitinates and degrades (1) components of the HRI-mediated signaling of the integrated stress response, such as DELE1 and EIF2AK1/HRI, as well as (2) unimported mitochondrial precursors such as ABHD10 (PubMed:38297121, PubMed:40328314). Within the SIFI complex, UBR4 initiates ubiquitin chains that are further elongated or branched by KCMF1 (PubMed:38297121, PubMed:40328314, PubMed:40875847). Mediates ubiquitination of ACLY, leading to its subsequent degradation (PubMed:23932781). Together with clathrin, forms meshwork structures involved in membrane morphogenesis and cytoskeletal organization (PubMed:16214886). {ECO:0000269|PubMed:16214886, ECO:0000269|PubMed:23932781, ECO:0000269|PubMed:25582440, ECO:0000269|PubMed:29033132, ECO:0000269|PubMed:34893540, ECO:0000269|PubMed:37891180, ECO:0000269|PubMed:38030679, ECO:0000269|PubMed:38182926, ECO:0000269|PubMed:38297121, ECO:0000269|PubMed:40328314, ECO:0000269|PubMed:40875847}.