E3 protein ligase that mediates ufmylation, the covalent attachment of the ubiquitin-like modifier UFM1 to lysine residues on target proteins, and which plays a key role in reticulophagy (also called ER-phagy) induced in response to endoplasmic reticulum stress (PubMed:20018847, PubMed:20164180, PubMed:20228063, PubMed:25219498, PubMed:32160526). In response to endoplasmic reticulum stress, recruited to the endoplasmic reticulum membrane by DDRGK1, and mediates ufmylation of proteins such as RPN1 and RPL26/uL24, thereby promoting reticulophagy of endoplasmic reticulum sheets (PubMed:32160526). Ufmylation-dependent reticulophagy inhibits the unfolded protein response (UPR) via ERN1/IRE1-alpha (PubMed:23152784, PubMed:32160526). Ufmylation in response to endoplasmic reticulum stress is essential for processes such as hematopoiesis, blood vessel morphogenesis or inflammatory response (PubMed:32050156). Regulates inflammation in response to endoplasmic reticulum stress by promoting reticulophagy, leading to inhibit the activity of the NF-kappa-B transcription factor (By similarity). Mediates ufmylation of DDRGK1 and CDK5RAP3; the role of these modifications is however unclear: as both DDRGK1 and CDK5RAP3 act as substrate adapters for ufmylation, it is uncertain whether ufmylation of these proteins is a collateral effect or is required for ufmylation (PubMed:20531390, PubMed:20018847). Catalyzes ufmylation of various subunits of the ribosomal complex or associated components, such as RPS3/uS3, RPS20/uS10, RPL10/uL16, RPL26/uL24 and EIF6 (By similarity). Anchors CDK5RAP3 in the cytoplasm, preventing its translocation to the nucleus which allows expression of the CCND1 cyclin and progression of cells through the G1/S transition (PubMed:20531390). Also involved in the response to DNA damage: recruited to double-strand break sites following DNA damage and mediates monoufmylation of histone H4 (PubMed:30886146). Catalyzes ufmylation of TRIP4, thereby playing a role in nuclear receptor-mediated transcription (PubMed:25219498). Required for hematopoietic stem cell function and hematopoiesis (By similarity). Required for cardiac homeostasis (By similarity). Interacts with DDRGK1 (via PCI domain) (PubMed:20018847, PubMed:20164180, PubMed:25219498, PubMed:32160526). Interacts with UFC1 (PubMed:20018847, PubMed:30886146). Interacts with RELA (PubMed:20164180). Interacts with TRIP4 (PubMed:25219498). Interacts with CDK5RAP3; the interaction is direct (PubMed:20164180, PubMed:20228063). Interacts with NBN; promoting recruitment to double-strand breaks following DNA damage (PubMed:30886146). Recruited to double-strand breaks by the MRE11-RAD50-NBN (MRN) complex following DNA damage. Ubiquitously expressed, with a high expression in liver (at protein level) (PubMed:20018847). Low expression in several invasive hepatocellular carcinomas, such Hep-G2, Hep 3B2.1-7, HLE and PLC (PubMed:20018847). Up-regulated by thapsigargin (PubMed:23152784). Down-regulated in the failing hearts of patients with dilated cardiomyopathy (PubMed:23152784). Ubiquitinated, leading to its degradation by the proteasome (PubMed:20164180). Interaction with CDK5RAP3 protects both proteins against ubiquitination and degradation via the proteasome (PubMed:20164180). Phosphorylated at Ser-462 by ATM, enhancing protein ligase activity and promoting ATM activation in a positive feedback loop. Belongs to the UFL1 family. Contaminating sequence. Potential poly-A sequence. Extended N-terminus.