{"gene":"UBR3","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":2011,"finding":"UBR3 is an E3 ubiquitin ligase that polyubiquitylates APE1 (Ref-1) at multiple lysine residues clustered on the N-terminal tail, controlling steady-state cellular levels of APE1; knockout of Ubr3 in mouse embryonic fibroblasts leads to up-regulation of APE1 protein and subsequent genomic instability.","method":"In vitro ubiquitylation assay, protein purification, Ubr3 knockout mouse embryonic fibroblasts with genomic instability readout","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro ubiquitylation assay identifying direct substrate with multiple orthogonal methods (biochemical purification, KO cellular phenotype), single lab","pmids":["21933813"],"is_preprint":false},{"year":2007,"finding":"UBR3 contains RING and UBR box domains similar to UBR1 and UBR2; E2 enzymes HR6A and HR6B, which bind UBR1 and UBR2, also physically interact with UBR3. However, unlike UBR1 and UBR2, UBR3 does not recognize N-end rule substrates.","method":"Binding assay (E2-E3 interaction), cloning and biochemical characterization, N-end rule substrate recognition assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct protein interaction assay and negative substrate recognition result, single lab with multiple methods","pmids":["17462990"],"is_preprint":false},{"year":2007,"finding":"UBR3 knockout mice (129SvImJ background) die during embryogenesis; C57BL/6 background Ubr3-/- mice show neonatal lethality, suckling impairment, and adult female-specific behavioral anosmia. LacZ reporter reveals UBR3 expression in olfactory pathway cells and cells of touch, vision, hearing, and taste systems.","method":"Ubr3 gene knockout mouse strains, LacZ reporter expression, behavioral phenotyping","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with defined cellular/behavioral phenotypes and localization data, single lab","pmids":["17462990"],"is_preprint":false},{"year":2016,"finding":"Drosophila Ubr3 (ortholog of mammalian UBR3) negatively regulates mono-ubiquitination of non-muscle Myosin II; mono-ubiquitinated Myosin II physically interacts with Myosin VIIa (responsible for Usher syndrome type IB). Ubr3 interacts genetically and physically with three Usher syndrome proteins, and the Myosin VIIa–Myosin IIa interaction is conserved in the mammalian cochlea and human retinal pigment epithelium cells.","method":"Forward genetic screen in Drosophila, Co-immunoprecipitation, ubiquitination assay, genetic epistasis, mammalian cochlea and human cell validation","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, genetic epistasis, cross-species functional validation, multiple orthogonal methods","pmids":["27331610"],"is_preprint":false},{"year":2016,"finding":"Drosophila Ubr3 (ortholog of mammalian UBR3) is a positive regulator of Hedgehog (Hh) signaling and promotes poly-ubiquitination and degradation of Cos2 (a central Hh signaling component). Mouse UBR3 poly-ubiquitinates Kif7, the mammalian homologue of Cos2; loss of UBR3 up-regulates Kif7 protein levels and decreases Hh signaling in cultured cells.","method":"Genetic screen in Drosophila, in vitro/cell-based ubiquitination assay, zebrafish loss-of-function, cultured cell knockdown, protein level measurement","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — direct ubiquitination assay, cross-species validation (Drosophila, zebrafish, mouse, cultured cells), multiple orthogonal methods","pmids":["27195754"],"is_preprint":false},{"year":2014,"finding":"Drosophila Ubr3 (ortholog of mammalian UBR3) physically interacts via its UBR-box domain with the neo-epitope of DIAP1 exposed after caspase-mediated cleavage, promoting recruitment and ubiquitination of substrate caspases by DIAP1 and thus positively regulating DIAP1 activity. This function is independent of the RING domain (E3 ligase activity). Loss of ubr3 causes caspase-dependent apoptosis, suppressible by loss of Dronc or ectopic p35 expression.","method":"Co-immunoprecipitation (UBR-box domain interaction), RING-domain mutant analysis, genetic epistasis (dronc loss-of-function, p35 overexpression), apoptosis assays in Drosophila eye and wing discs","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, domain mutagenesis, genetic epistasis with multiple suppressors, single lab with multiple orthogonal methods","pmids":["25146930"],"is_preprint":false},{"year":2019,"finding":"Ubr3 (Drosophila/insect ortholog of mammalian UBR3) forms a molecular complex with Mlpt micropeptides and transcription factor Shavenbaby (Svb) that constitutes an ancient developmental module for embryo patterning; this complex is required for early insect embryo segmentation.","method":"Genetic interaction studies, loss-of-function analysis in Drosophila and Tribolium, restoration-of-function epistasis experiments","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis and loss-of-function across species with defined patterning phenotype, single lab","pmids":["30896406"],"is_preprint":false},{"year":2015,"finding":"UBR3 (and UBR6) regulate cardiac Nav1.5 channel protein levels via the ubiquitin-proteasome pathway; knockdown of UBR3 increases Nav1.5 protein and ubiquitylation, enhances Nav1.5 channel opening, and increases action potential amplitude. The effect is abolished by proteasome inhibition and is post-translational (not transcriptional).","method":"siRNA knockdown in neonatal rat ventricular myocytes and HEK293T cells, proteasome inhibitor experiments, ubiquitylation assay, electrophysiological recordings","journal":"Journal of cellular and molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — knockdown with defined electrophysiological phenotype, ubiquitylation assay, pharmacological rescue, single lab","pmids":["26059563"],"is_preprint":false},{"year":2020,"finding":"UBR3 (and UBR6) modulate cardiac Ca2+-induced Ca2+ release (CICR) by targeting Cav1.2 (L-type Ca2+ channel alpha1C subunit) for proteasomal degradation; knockdown of UBR3 increases Cav1.2 protein levels and enhances Cav1.2 channel current and SR Ca2+ release amplitude without affecting RyR2, SERCA2a, or PLB levels.","method":"siRNA knockdown in neonatal rat ventricular myocytes, protein level measurement, cycloheximide chase, electrophysiological recordings, Ca2+ imaging","journal":"Channels (Austin, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — knockdown with specific substrate (Cav1.2) identified, degradative regulation confirmed by protein synthesis inhibitor, electrophysiological validation, single lab","pmids":["32988261"],"is_preprint":false},{"year":2022,"finding":"UBR3 promotes ubiquitination of DUSP1 in nucleus pulposus cells; this leads to reduced DUSP1 activity, sustained p38 MAPK activation, and enhanced inflammation and apoptosis. Co-immunoprecipitation confirmed the UBR3–DUSP1 physical interaction; overexpression of DUSP1 reversed the pro-apoptotic/pro-inflammatory effects of UBR3 overexpression.","method":"Co-immunoprecipitation, siRNA knockdown and overexpression in nucleus pulposus cells, ubiquitination assay, rescue by DUSP1 overexpression, p38 phosphorylation readout","journal":"Human cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP identifying direct substrate, ubiquitination assay, rescue experiment, single lab with multiple orthogonal methods","pmids":["35332432"],"is_preprint":false}],"current_model":"UBR3 is a RING- and UBR-box-containing E3 ubiquitin ligase that, while unable to recognize canonical N-end rule substrates, binds E2 enzymes HR6A/HR6B and polyubiquitylates multiple substrates including APE1 (controlling DNA repair capacity and genome stability), Kif7/Cos2 (modulating Hedgehog signaling), Nav1.5 and Cav1.2 (regulating cardiac ion channel levels and electrophysiology), and DUSP1 (controlling p38 MAPK activity and inflammation); additionally, through its UBR-box domain (independently of RING/E3 ligase activity), UBR3 interacts with cleaved DIAP1 to promote caspase ubiquitination and anti-apoptotic signaling, and it negatively regulates Myosin II mono-ubiquitination to control auditory organ development."},"narrative":{"mechanistic_narrative":"UBR3 is a RING- and UBR-box-containing E3 ubiquitin ligase that controls the abundance of diverse substrates by targeting them for ubiquitin-dependent degradation, thereby shaping DNA repair, developmental signaling, cardiac excitability, and apoptosis [PMID:21933813, PMID:27195754, PMID:26059563]. Although it possesses the UBR-box shared with the N-recognins UBR1 and UBR2 and binds the same E2 enzymes HR6A/HR6B, UBR3 does not recognize canonical N-end rule substrates [PMID:17462990]. Its catalytic activity polyubiquitylates the DNA-repair enzyme APE1 to set its steady-state level, with loss of UBR3 causing APE1 accumulation and genomic instability [PMID:21933813]. UBR3 also positively regulates Hedgehog signaling by polyubiquitylating and degrading the kinesin Cos2/Kif7 [PMID:27195754], and post-translationally lowers cardiac ion channel levels by targeting Nav1.5 and the Cav1.2 L-type Ca2+ channel for proteasomal degradation, thereby tuning action potential amplitude and Ca2+-induced Ca2+ release [PMID:26059563, PMID:32988261]. In nucleus pulposus cells it ubiquitylates DUSP1 to sustain p38 MAPK activation and drive inflammation and apoptosis [PMID:35332432]. Independently of its RING/E3 activity, the UBR-box domain binds the caspase-cleaved neo-epitope of DIAP1 to promote caspase ubiquitination and anti-apoptotic signaling [PMID:25146930], and UBR3 negatively regulates mono-ubiquitination of non-muscle Myosin II, linking it to the Myosin VIIa-based Usher syndrome machinery during auditory and sensory organ development [PMID:27331610]. Knockout mice die during embryogenesis or perinatally and display sensory-system expression and defects, consistent with broad developmental requirements [PMID:17462990].","teleology":[{"year":2007,"claim":"Established that UBR3 belongs to the UBR-box/RING N-recognin family yet is mechanistically distinct, answering whether it acts via the same E2 partners and substrate logic as UBR1/UBR2.","evidence":"Cloning, E2-E3 binding assays with HR6A/HR6B, and N-end rule substrate recognition assays","pmids":["17462990"],"confidence":"Medium","gaps":["Did not identify any bona fide substrate","Left the functional role of the UBR-box undefined given absence of N-end rule recognition"]},{"year":2007,"claim":"Defined the in vivo requirement for UBR3 by showing embryonic/perinatal lethality and sensory-system expression, framing it as a developmentally essential ligase.","evidence":"Ubr3 knockout mouse strains, LacZ reporter expression, and behavioral phenotyping","pmids":["17462990"],"confidence":"Medium","gaps":["Did not connect phenotypes to specific molecular substrates","Background-dependent severity not mechanistically explained"]},{"year":2011,"claim":"Identified the first direct UBR3 substrate, APE1, explaining how the ligase couples ubiquitin-dependent turnover to DNA repair capacity and genome stability.","evidence":"In vitro ubiquitylation assays, protein purification, and Ubr3 knockout MEFs scored for genomic instability","pmids":["21933813"],"confidence":"High","gaps":["Did not map which E2 drives APE1 ubiquitylation in cells","Did not establish whether APE1 misregulation underlies the organismal phenotypes"]},{"year":2014,"claim":"Revealed a RING-independent, UBR-box-mediated function in apoptosis control, showing UBR3 can act as an adaptor rather than a catalytic ligase.","evidence":"Co-IP of the UBR-box with cleaved DIAP1, RING-domain mutant analysis, and genetic epistasis with dronc and p35 in Drosophila","pmids":["25146930"],"confidence":"High","gaps":["Mammalian counterpart of the DIAP1 interaction not demonstrated","How UBR-box recognizes the cleaved neo-epitope structurally unresolved"]},{"year":2016,"claim":"Linked UBR3 to two developmental axes — positive regulation of Hedgehog signaling via degradation of Cos2/Kif7, and negative regulation of Myosin II mono-ubiquitination connecting it to Usher syndrome proteins.","evidence":"Drosophila genetic screens, in vitro/cell ubiquitination assays, zebrafish and mouse loss-of-function, reciprocal Co-IP and cross-species cochlea/RPE validation","pmids":["27195754","27331610"],"confidence":"High","gaps":["Did not resolve how a single ligase produces both poly- and mono-ubiquitination outcomes on different substrates","Direct mammalian Kif7 ubiquitylation in vivo not fully dissected"]},{"year":2015,"claim":"Extended UBR3 substrate control to cardiac electrophysiology by showing post-translational, proteasome-dependent regulation of the Nav1.5 sodium channel.","evidence":"siRNA knockdown in neonatal rat ventricular myocytes and HEK293T cells, proteasome inhibition, ubiquitylation assay, and electrophysiology","pmids":["26059563"],"confidence":"Medium","gaps":["Direct ligase-substrate contact not shown by reconstitution","Physiological consequence at the whole-heart level untested"]},{"year":2020,"claim":"Showed a second cardiac substrate, Cav1.2, establishing UBR3 as a regulator of Ca2+-induced Ca2+ release with selectivity over other handling proteins.","evidence":"siRNA knockdown, cycloheximide chase, electrophysiology and Ca2+ imaging in neonatal rat ventricular myocytes","pmids":["32988261"],"confidence":"Medium","gaps":["Direct ubiquitylation of Cav1.2 by purified UBR3 not reconstituted","In vivo cardiac relevance not addressed"]},{"year":2022,"claim":"Connected UBR3 to inflammatory signaling by showing ubiquitylation of the phosphatase DUSP1 sustains p38 MAPK activity and drives apoptosis/inflammation.","evidence":"Co-IP, knockdown/overexpression in nucleus pulposus cells, ubiquitination assay, and DUSP1 rescue","pmids":["35332432"],"confidence":"Medium","gaps":["Ubiquitin linkage type and whether DUSP1 is degraded vs inactivated not fully defined","Generality beyond nucleus pulposus cells untested"]},{"year":2019,"claim":"Placed UBR3 in an ancient developmental patterning module with Mlpt micropeptides and Shavenbaby, broadening its role beyond degradative ubiquitination.","evidence":"Genetic interaction and loss/restoration-of-function studies in Drosophila and Tribolium","pmids":["30896406"],"confidence":"Medium","gaps":["Biochemical nature of the Ubr3-Mlpt-Svb complex not defined","Whether catalytic activity is required within this module unknown"]},{"year":null,"claim":"It remains unresolved how UBR3 achieves substrate selectivity across such diverse targets and how its catalytic (RING) versus adaptor (UBR-box) modes are partitioned in mammalian tissues.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural basis for substrate recognition reported","Degron/recognition determinants on substrates unmapped","Tissue-specific cofactors directing different substrates unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,4,9]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,4,7,8,9]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[5]}],"localization":[],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,4,7,8,9]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3,4]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[5,9]}],"complexes":["Ubr3-Mlpt-Shavenbaby developmental module"],"partners":["HR6A","HR6B","DIAP1","DUSP1","KIF7","CAV1.2","NAV1.5"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6ZT12","full_name":"E3 ubiquitin-protein ligase UBR3","aliases":["N-recognin-3","RING-type E3 ubiquitin transferase UBR3","Ubiquitin-protein ligase E3-alpha-3","Ubiquitin-protein ligase E3-alpha-III","Zinc finger protein 650"],"length_aa":1888,"mass_kda":212.4,"function":"E3 ubiquitin-protein ligase which is a component of the N-end rule pathway (By similarity). Does not bind to proteins bearing specific N-terminal residues that are destabilizing according to the N-end rule, leading to their ubiquitination and subsequent degradation (By similarity). May play a role in Shh signaling by mediating the ubiquitination of Kif7 (By similarity). May be important for MYH9 function in certain tissues, possibly by regulating the ubiquitination of MYH9 and consequently affecting its interaction with MYO7A (PubMed:27331610)","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/Q6ZT12/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/UBR3","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/UBR3","total_profiled":1310},"omim":[{"mim_id":"613831","title":"UBIQUITIN PROTEIN LIGASE E3 COMPONENT N-RECOGNIN 3; UBR3","url":"https://www.omim.org/entry/613831"},{"mim_id":"609890","title":"UBIQUITIN PROTEIN LIGASE E3 COMPONENT N-RECOGNIN 4; UBR4","url":"https://www.omim.org/entry/609890"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Nucleoli","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"skeletal muscle","ntpm":68.6},{"tissue":"tongue","ntpm":81.3}],"url":"https://www.proteinatlas.org/search/UBR3"},"hgnc":{"alias_symbol":["KIAA2024","DKFZp434P117","FLJ37422"],"prev_symbol":["ZNF650"]},"alphafold":{"accession":"Q6ZT12","domains":[{"cath_id":"-","chopping":"46-58_89-118_198-229_237-284_382-407","consensus_level":"medium","plddt":83.7272,"start":46,"end":407},{"cath_id":"2.10.110.30","chopping":"120-183","consensus_level":"high","plddt":79.5931,"start":120,"end":183},{"cath_id":"-","chopping":"1311-1377_1392-1514_1529-1622_1638-1737","consensus_level":"medium","plddt":85.8204,"start":1311,"end":1737},{"cath_id":"-","chopping":"1747-1888","consensus_level":"medium","plddt":85.508,"start":1747,"end":1888}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6ZT12","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6ZT12-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6ZT12-F1-predicted_aligned_error_v6.png","plddt_mean":77.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=UBR3","jax_strain_url":"https://www.jax.org/strain/search?query=UBR3"},"sequence":{"accession":"Q6ZT12","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6ZT12.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6ZT12/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6ZT12"}},"corpus_meta":[{"pmid":"21933813","id":"PMC_21933813","title":"Ubiquitin ligase UBR3 regulates cellular levels of the essential DNA repair protein APE1 and is required for genome stability.","date":"2011","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/21933813","citation_count":55,"is_preprint":false},{"pmid":"17462990","id":"PMC_17462990","title":"Biochemical and genetic studies of UBR3, a ubiquitin ligase with a function in olfactory and other sensory systems.","date":"2007","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17462990","citation_count":45,"is_preprint":false},{"pmid":"27331610","id":"PMC_27331610","title":"The E3 ligase Ubr3 regulates Usher syndrome and MYH9 disorder proteins in the auditory organs of Drosophila and mammals.","date":"2016","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/27331610","citation_count":25,"is_preprint":false},{"pmid":"30896406","id":"PMC_30896406","title":"The mlpt/Ubr3/Svb module comprises an ancient developmental switch for embryonic patterning.","date":"2019","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/30896406","citation_count":21,"is_preprint":false},{"pmid":"25146930","id":"PMC_25146930","title":"Ubr3 E3 ligase regulates apoptosis by controlling the activity of DIAP1 in Drosophila.","date":"2014","source":"Cell death and differentiation","url":"https://pubmed.ncbi.nlm.nih.gov/25146930","citation_count":20,"is_preprint":false},{"pmid":"27195754","id":"PMC_27195754","title":"Ubr3, a Novel Modulator of Hh Signaling Affects the Degradation of Costal-2 and Kif7 through Poly-ubiquitination.","date":"2016","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/27195754","citation_count":17,"is_preprint":false},{"pmid":"26059563","id":"PMC_26059563","title":"Cardiac Nav 1.5 is modulated by ubiquitin protein ligase E3 component n-recognin UBR3 and 6.","date":"2015","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/26059563","citation_count":15,"is_preprint":false},{"pmid":"35332432","id":"PMC_35332432","title":"UBR3 promotes inflammation and apoptosis via DUSP1/p38 pathway in the nucleus pulposus cells of patients with intervertebral disc degeneration.","date":"2022","source":"Human cell","url":"https://pubmed.ncbi.nlm.nih.gov/35332432","citation_count":12,"is_preprint":false},{"pmid":"32988261","id":"PMC_32988261","title":"Modulation of Ca2+-induced Ca2+ release by ubiquitin protein ligase E3 component n-recognin UBR3 and 6 in cardiac myocytes.","date":"2020","source":"Channels (Austin, Tex.)","url":"https://pubmed.ncbi.nlm.nih.gov/32988261","citation_count":8,"is_preprint":false},{"pmid":"32344861","id":"PMC_32344861","title":"Breakpoint Mapping of Symptomatic Balanced Translocations Links the EPHA6, KLF13 and UBR3 Genes to Novel Disease Phenotype.","date":"2020","source":"Journal of clinical medicine","url":"https://pubmed.ncbi.nlm.nih.gov/32344861","citation_count":6,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.02.24.639925","title":"Whole-genome sequencing analysis of anthropometric traits in 672,976 individuals reveals convergence between rare and common genetic associations","date":"2025-02-25","source":"bioRxiv","url":"https://doi.org/10.1101/2025.02.24.639925","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7628,"output_tokens":2826,"usd":0.032637,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10083,"output_tokens":3328,"usd":0.066808,"stage2_stop_reason":"end_turn"},"total_usd":0.099445,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2011,\n      \"finding\": \"UBR3 is an E3 ubiquitin ligase that polyubiquitylates APE1 (Ref-1) at multiple lysine residues clustered on the N-terminal tail, controlling steady-state cellular levels of APE1; knockout of Ubr3 in mouse embryonic fibroblasts leads to up-regulation of APE1 protein and subsequent genomic instability.\",\n      \"method\": \"In vitro ubiquitylation assay, protein purification, Ubr3 knockout mouse embryonic fibroblasts with genomic instability readout\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro ubiquitylation assay identifying direct substrate with multiple orthogonal methods (biochemical purification, KO cellular phenotype), single lab\",\n      \"pmids\": [\"21933813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"UBR3 contains RING and UBR box domains similar to UBR1 and UBR2; E2 enzymes HR6A and HR6B, which bind UBR1 and UBR2, also physically interact with UBR3. However, unlike UBR1 and UBR2, UBR3 does not recognize N-end rule substrates.\",\n      \"method\": \"Binding assay (E2-E3 interaction), cloning and biochemical characterization, N-end rule substrate recognition assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct protein interaction assay and negative substrate recognition result, single lab with multiple methods\",\n      \"pmids\": [\"17462990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"UBR3 knockout mice (129SvImJ background) die during embryogenesis; C57BL/6 background Ubr3-/- mice show neonatal lethality, suckling impairment, and adult female-specific behavioral anosmia. LacZ reporter reveals UBR3 expression in olfactory pathway cells and cells of touch, vision, hearing, and taste systems.\",\n      \"method\": \"Ubr3 gene knockout mouse strains, LacZ reporter expression, behavioral phenotyping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined cellular/behavioral phenotypes and localization data, single lab\",\n      \"pmids\": [\"17462990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Drosophila Ubr3 (ortholog of mammalian UBR3) negatively regulates mono-ubiquitination of non-muscle Myosin II; mono-ubiquitinated Myosin II physically interacts with Myosin VIIa (responsible for Usher syndrome type IB). Ubr3 interacts genetically and physically with three Usher syndrome proteins, and the Myosin VIIa–Myosin IIa interaction is conserved in the mammalian cochlea and human retinal pigment epithelium cells.\",\n      \"method\": \"Forward genetic screen in Drosophila, Co-immunoprecipitation, ubiquitination assay, genetic epistasis, mammalian cochlea and human cell validation\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, genetic epistasis, cross-species functional validation, multiple orthogonal methods\",\n      \"pmids\": [\"27331610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Drosophila Ubr3 (ortholog of mammalian UBR3) is a positive regulator of Hedgehog (Hh) signaling and promotes poly-ubiquitination and degradation of Cos2 (a central Hh signaling component). Mouse UBR3 poly-ubiquitinates Kif7, the mammalian homologue of Cos2; loss of UBR3 up-regulates Kif7 protein levels and decreases Hh signaling in cultured cells.\",\n      \"method\": \"Genetic screen in Drosophila, in vitro/cell-based ubiquitination assay, zebrafish loss-of-function, cultured cell knockdown, protein level measurement\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — direct ubiquitination assay, cross-species validation (Drosophila, zebrafish, mouse, cultured cells), multiple orthogonal methods\",\n      \"pmids\": [\"27195754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Drosophila Ubr3 (ortholog of mammalian UBR3) physically interacts via its UBR-box domain with the neo-epitope of DIAP1 exposed after caspase-mediated cleavage, promoting recruitment and ubiquitination of substrate caspases by DIAP1 and thus positively regulating DIAP1 activity. This function is independent of the RING domain (E3 ligase activity). Loss of ubr3 causes caspase-dependent apoptosis, suppressible by loss of Dronc or ectopic p35 expression.\",\n      \"method\": \"Co-immunoprecipitation (UBR-box domain interaction), RING-domain mutant analysis, genetic epistasis (dronc loss-of-function, p35 overexpression), apoptosis assays in Drosophila eye and wing discs\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, domain mutagenesis, genetic epistasis with multiple suppressors, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"25146930\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Ubr3 (Drosophila/insect ortholog of mammalian UBR3) forms a molecular complex with Mlpt micropeptides and transcription factor Shavenbaby (Svb) that constitutes an ancient developmental module for embryo patterning; this complex is required for early insect embryo segmentation.\",\n      \"method\": \"Genetic interaction studies, loss-of-function analysis in Drosophila and Tribolium, restoration-of-function epistasis experiments\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis and loss-of-function across species with defined patterning phenotype, single lab\",\n      \"pmids\": [\"30896406\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"UBR3 (and UBR6) regulate cardiac Nav1.5 channel protein levels via the ubiquitin-proteasome pathway; knockdown of UBR3 increases Nav1.5 protein and ubiquitylation, enhances Nav1.5 channel opening, and increases action potential amplitude. The effect is abolished by proteasome inhibition and is post-translational (not transcriptional).\",\n      \"method\": \"siRNA knockdown in neonatal rat ventricular myocytes and HEK293T cells, proteasome inhibitor experiments, ubiquitylation assay, electrophysiological recordings\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — knockdown with defined electrophysiological phenotype, ubiquitylation assay, pharmacological rescue, single lab\",\n      \"pmids\": [\"26059563\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"UBR3 (and UBR6) modulate cardiac Ca2+-induced Ca2+ release (CICR) by targeting Cav1.2 (L-type Ca2+ channel alpha1C subunit) for proteasomal degradation; knockdown of UBR3 increases Cav1.2 protein levels and enhances Cav1.2 channel current and SR Ca2+ release amplitude without affecting RyR2, SERCA2a, or PLB levels.\",\n      \"method\": \"siRNA knockdown in neonatal rat ventricular myocytes, protein level measurement, cycloheximide chase, electrophysiological recordings, Ca2+ imaging\",\n      \"journal\": \"Channels (Austin, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — knockdown with specific substrate (Cav1.2) identified, degradative regulation confirmed by protein synthesis inhibitor, electrophysiological validation, single lab\",\n      \"pmids\": [\"32988261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"UBR3 promotes ubiquitination of DUSP1 in nucleus pulposus cells; this leads to reduced DUSP1 activity, sustained p38 MAPK activation, and enhanced inflammation and apoptosis. Co-immunoprecipitation confirmed the UBR3–DUSP1 physical interaction; overexpression of DUSP1 reversed the pro-apoptotic/pro-inflammatory effects of UBR3 overexpression.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown and overexpression in nucleus pulposus cells, ubiquitination assay, rescue by DUSP1 overexpression, p38 phosphorylation readout\",\n      \"journal\": \"Human cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP identifying direct substrate, ubiquitination assay, rescue experiment, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"35332432\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"UBR3 is a RING- and UBR-box-containing E3 ubiquitin ligase that, while unable to recognize canonical N-end rule substrates, binds E2 enzymes HR6A/HR6B and polyubiquitylates multiple substrates including APE1 (controlling DNA repair capacity and genome stability), Kif7/Cos2 (modulating Hedgehog signaling), Nav1.5 and Cav1.2 (regulating cardiac ion channel levels and electrophysiology), and DUSP1 (controlling p38 MAPK activity and inflammation); additionally, through its UBR-box domain (independently of RING/E3 ligase activity), UBR3 interacts with cleaved DIAP1 to promote caspase ubiquitination and anti-apoptotic signaling, and it negatively regulates Myosin II mono-ubiquitination to control auditory organ development.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"UBR3 is a RING- and UBR-box-containing E3 ubiquitin ligase that controls the abundance of diverse substrates by targeting them for ubiquitin-dependent degradation, thereby shaping DNA repair, developmental signaling, cardiac excitability, and apoptosis [#0, #4, #7]. Although it possesses the UBR-box shared with the N-recognins UBR1 and UBR2 and binds the same E2 enzymes HR6A/HR6B, UBR3 does not recognize canonical N-end rule substrates [#1]. Its catalytic activity polyubiquitylates the DNA-repair enzyme APE1 to set its steady-state level, with loss of UBR3 causing APE1 accumulation and genomic instability [#0]. UBR3 also positively regulates Hedgehog signaling by polyubiquitylating and degrading the kinesin Cos2/Kif7 [#4], and post-translationally lowers cardiac ion channel levels by targeting Nav1.5 and the Cav1.2 L-type Ca2+ channel for proteasomal degradation, thereby tuning action potential amplitude and Ca2+-induced Ca2+ release [#7, #8]. In nucleus pulposus cells it ubiquitylates DUSP1 to sustain p38 MAPK activation and drive inflammation and apoptosis [#9]. Independently of its RING/E3 activity, the UBR-box domain binds the caspase-cleaved neo-epitope of DIAP1 to promote caspase ubiquitination and anti-apoptotic signaling [#5], and UBR3 negatively regulates mono-ubiquitination of non-muscle Myosin II, linking it to the Myosin VIIa-based Usher syndrome machinery during auditory and sensory organ development [#3]. Knockout mice die during embryogenesis or perinatally and display sensory-system expression and defects, consistent with broad developmental requirements [#2].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Established that UBR3 belongs to the UBR-box/RING N-recognin family yet is mechanistically distinct, answering whether it acts via the same E2 partners and substrate logic as UBR1/UBR2.\",\n      \"evidence\": \"Cloning, E2-E3 binding assays with HR6A/HR6B, and N-end rule substrate recognition assays\",\n      \"pmids\": [\"17462990\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not identify any bona fide substrate\", \"Left the functional role of the UBR-box undefined given absence of N-end rule recognition\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defined the in vivo requirement for UBR3 by showing embryonic/perinatal lethality and sensory-system expression, framing it as a developmentally essential ligase.\",\n      \"evidence\": \"Ubr3 knockout mouse strains, LacZ reporter expression, and behavioral phenotyping\",\n      \"pmids\": [\"17462990\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not connect phenotypes to specific molecular substrates\", \"Background-dependent severity not mechanistically explained\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified the first direct UBR3 substrate, APE1, explaining how the ligase couples ubiquitin-dependent turnover to DNA repair capacity and genome stability.\",\n      \"evidence\": \"In vitro ubiquitylation assays, protein purification, and Ubr3 knockout MEFs scored for genomic instability\",\n      \"pmids\": [\"21933813\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not map which E2 drives APE1 ubiquitylation in cells\", \"Did not establish whether APE1 misregulation underlies the organismal phenotypes\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Revealed a RING-independent, UBR-box-mediated function in apoptosis control, showing UBR3 can act as an adaptor rather than a catalytic ligase.\",\n      \"evidence\": \"Co-IP of the UBR-box with cleaved DIAP1, RING-domain mutant analysis, and genetic epistasis with dronc and p35 in Drosophila\",\n      \"pmids\": [\"25146930\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian counterpart of the DIAP1 interaction not demonstrated\", \"How UBR-box recognizes the cleaved neo-epitope structurally unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Linked UBR3 to two developmental axes — positive regulation of Hedgehog signaling via degradation of Cos2/Kif7, and negative regulation of Myosin II mono-ubiquitination connecting it to Usher syndrome proteins.\",\n      \"evidence\": \"Drosophila genetic screens, in vitro/cell ubiquitination assays, zebrafish and mouse loss-of-function, reciprocal Co-IP and cross-species cochlea/RPE validation\",\n      \"pmids\": [\"27195754\", \"27331610\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve how a single ligase produces both poly- and mono-ubiquitination outcomes on different substrates\", \"Direct mammalian Kif7 ubiquitylation in vivo not fully dissected\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Extended UBR3 substrate control to cardiac electrophysiology by showing post-translational, proteasome-dependent regulation of the Nav1.5 sodium channel.\",\n      \"evidence\": \"siRNA knockdown in neonatal rat ventricular myocytes and HEK293T cells, proteasome inhibition, ubiquitylation assay, and electrophysiology\",\n      \"pmids\": [\"26059563\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ligase-substrate contact not shown by reconstitution\", \"Physiological consequence at the whole-heart level untested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed a second cardiac substrate, Cav1.2, establishing UBR3 as a regulator of Ca2+-induced Ca2+ release with selectivity over other handling proteins.\",\n      \"evidence\": \"siRNA knockdown, cycloheximide chase, electrophysiology and Ca2+ imaging in neonatal rat ventricular myocytes\",\n      \"pmids\": [\"32988261\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ubiquitylation of Cav1.2 by purified UBR3 not reconstituted\", \"In vivo cardiac relevance not addressed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Connected UBR3 to inflammatory signaling by showing ubiquitylation of the phosphatase DUSP1 sustains p38 MAPK activity and drives apoptosis/inflammation.\",\n      \"evidence\": \"Co-IP, knockdown/overexpression in nucleus pulposus cells, ubiquitination assay, and DUSP1 rescue\",\n      \"pmids\": [\"35332432\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitin linkage type and whether DUSP1 is degraded vs inactivated not fully defined\", \"Generality beyond nucleus pulposus cells untested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Placed UBR3 in an ancient developmental patterning module with Mlpt micropeptides and Shavenbaby, broadening its role beyond degradative ubiquitination.\",\n      \"evidence\": \"Genetic interaction and loss/restoration-of-function studies in Drosophila and Tribolium\",\n      \"pmids\": [\"30896406\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Biochemical nature of the Ubr3-Mlpt-Svb complex not defined\", \"Whether catalytic activity is required within this module unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how UBR3 achieves substrate selectivity across such diverse targets and how its catalytic (RING) versus adaptor (UBR-box) modes are partitioned in mammalian tissues.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural basis for substrate recognition reported\", \"Degron/recognition determinants on substrates unmapped\", \"Tissue-specific cofactors directing different substrates unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 4, 9]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 4, 7, 8, 9]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 4, 7, 8, 9]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [5, 9]}\n    ],\n    \"complexes\": [\"Ubr3-Mlpt-Shavenbaby developmental module\"],\n    \"partners\": [\"HR6A\", \"HR6B\", \"DIAP1\", \"DUSP1\", \"Kif7\", \"Cav1.2\", \"Nav1.5\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}