{"gene":"LIG3","run_date":"2026-06-10T02:59:49","timeline":{"discoveries":[{"year":2013,"finding":"The LIG3 gene encodes multiple DNA ligase polypeptides: the only mitochondrial DNA ligase (essential for that organelle), and nuclear DNA ligase IIIα which partners with XRCC1 in base excision repair (BER) and single-strand break repair. Nuclear LIG3α also functions in an alternative NHEJ (alt-NHEJ) pathway for DSB repair that is independent of its XRCC1 interaction, and can substitute for LIG1 in DNA replication when LIG1 is absent.","method":"Review synthesizing genetic, biochemical, and cell biological experiments across multiple studies","journal":"Gene","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal experimental approaches replicated across labs, including KO/knockdown, in vitro assays, and complementation studies","pmids":["24013086"],"is_preprint":false},{"year":2021,"finding":"LIG3-XRCC1 complex serves as a backup system for Okazaki fragment ligation when LIG1 is absent. PARP1-HPF1-dependent ADP-ribosylation of histone H3 is required to recruit LIG3 onto chromatin for this backup ligation; depletion of PARP1 or HPF1 prevents LIG3 chromatin recruitment and Okazaki fragment joining in the absence of LIG1.","method":"Cell-free system from Xenopus egg extracts with immunodepletion of LIG1, PARP1, HPF1, and XRCC1; chromatin fractionation; ADP-ribosylation assays","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — reconstitution in cell-free system with multiple depletions and orthogonal biochemical readouts in a single rigorous study","pmids":["33872376"],"is_preprint":false},{"year":2021,"finding":"RAD52 inhibits single-strand break repair (SSBR) by reducing DNA-damage-promoted co-localization of XRCC1 and LIG3α at repair foci, via RAD52's high-affinity binding to single-stranded DNA (ssDNA) and poly(ADP-ribose) (PAR).","method":"Co-localization/imaging of XRCC1/LIG3α foci, RAD52 knockout/knockdown, camptothecin treatment, ssDNA and PAR binding assays, cell survival assays","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (imaging, binding assays, KO) in a single lab","pmids":["33440161"],"is_preprint":false},{"year":2018,"finding":"MALAT1 lncRNA physically binds PARP1 and LIG3 and is a component of the alternative NHEJ (A-NHEJ) protein complex in multiple myeloma cells; degradation of MALAT1 by antisense oligonucleotides disrupts this complex, increases poly-ADP-ribosylation of nuclear proteins, and defects the DNA repair pathway leading to apoptosis.","method":"RNA-protein binding (co-immunoprecipitation of MALAT1 with PARP1/LIG3), antisense gapmer knockdown, in vitro and in vivo (xenograft) functional assays","journal":"Leukemia","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — RNA-protein pulldown combined with functional knockdown and in vivo validation; single lab","pmids":["29632340"],"is_preprint":false},{"year":2015,"finding":"c-MYC transcriptionally activates LIG3 and PARP1 expression in BCR-ABL1- and FLT3/ITD-driven leukemias. c-MYC negatively regulates miR-150 and miR-22, which in turn suppress LIG3 and PARP1, driving increased alt-NHEJ activity and genomic instability.","method":"c-MYC inhibition, miRNA overexpression (miR-150, miR-22), gene expression analysis in primary and cultured leukemia cells and patient samples, alt-NHEJ activity assays","journal":"Molecular cancer research : MCR","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple complementary approaches (inhibitor, miRNA OE, patient samples) in a single lab","pmids":["25828893"],"is_preprint":false},{"year":2016,"finding":"Telomere-internal double-strand breaks are repaired by a PARP1- and LIG3-dependent end-joining reaction consistent with alt-NHEJ or single-strand break repair, in addition to homologous recombination.","method":"FokI-induced DSBs at telomeres, genetic depletion of PARP1 and LIG3, telomere FISH and imaging, microhomology analysis","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic depletion with specific functional readout (telomere repair), single lab","pmids":["27806302"],"is_preprint":false},{"year":2021,"finding":"Biallelic loss-of-function variants in LIG3 cause mitochondrial DNA depletion (without multiple deletions), impair mtDNA maintenance, and result in mitochondrial dysfunction manifesting as a neurogastrointestinal encephalomyopathy syndrome. Patient-derived cells show reduced LIG3 protein and ligase activity; disruption of lig3 in zebrafish reproduces brain alterations and gut transit impairment.","method":"Whole exome sequencing, in vitro ligase activity assays in patient cells, zebrafish lig3 disruption model, mtDNA copy number quantification, muscle biopsy/COX staining","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro functional assays, multiple patient families, zebrafish model replication; multiple orthogonal methods","pmids":["33855352"],"is_preprint":false},{"year":2019,"finding":"Sirt3 deacetylates LIG3 protein (along with other BER enzymes NEIL1, NEIL2, OGG1, MUTYH, APE1) in mitochondria; LIG3 is a substrate for Sirt3-mediated deacetylation, which modulates LIG3 activity in the mitochondrial BER pathway.","method":"Deacetylation assay with Sirt3 and BER substrates including LIG3 in colorectal cancer cells","journal":"Polski przeglad chirurgiczny","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single enzymatic assay, single lab, limited methodological detail in abstract","pmids":["32312920"],"is_preprint":false},{"year":2025,"finding":"Nuclear LIG3 is recruited to NHEJ complexes to facilitate end joining in the presence (but not catalytic activity) of LIG4. Mice lacking nuclear LIG3 and expressing catalytically inactive LIG4 die as embryos (lethal genetic interaction), whereas nuclear LIG3-deficient mice alone are viable, demonstrating that LIG3 substitutes for LIG4 catalytic activity in NHEJ when LIG4 is present as a structural scaffold.","method":"Mouse genetics: nuclear Lig3 knockout strain crossed to Lig4 catalytic-dead knock-in; timed mating/embryo resorption analysis; lymphocyte development assays","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic epistasis with two independent mouse strains, embryonic lethality as definitive readout, rigorous genetic interaction","pmids":["39673806"],"is_preprint":false},{"year":2025,"finding":"LIG3 (with PARP1) performs an alternative Okazaki fragment maturation (OFM) process: when FEN1 demethylation by JMJD1B and subsequent LIG1 recruitment is disrupted, unprocessed 5' flaps trigger PARP1-dependent LIG3 recruitment to join incompletely processed Okazaki fragments. LIG3 has flap ligation activity in this context, supporting cell survival but causing duplications and mutations.","method":"Cell-based genetic disruption of JMJD1B and FEN1 R192Q mutation; PARP1 inhibition; PCNA binding assays; mutagenesis/sequencing","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple genetic and biochemical approaches in single preprint lab; not yet peer-reviewed","pmids":["41280084"],"is_preprint":true},{"year":2025,"finding":"LIG3α exhibits an inability to ligate polβ dCTP:8-oxoG insertion products (error-free repair intermediates) at the final BER step, while it can seal nicks from polβ mutagenic dATP insertion opposite 8-oxoG. This demonstrates that the identity of the BER ligase critically determines repair outcome (mutagenic vs. error-free) at the ligation step.","method":"In vitro ligation assays with purified LIG1 and LIG3α on defined nick substrates containing polβ insertion products opposite 8-oxoG","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro reconstitution with defined substrates, single lab, single study","pmids":["40286853"],"is_preprint":false},{"year":2025,"finding":"YY1-Lig3-PARP1 form a complex in which Lig3 catalyzes DNA religation after YY1-mediated DNA looping to drive extrachromosomal DNA (ecDNA) biogenesis. PARylation-dependent acidic microenvironments mediated by the Lig3-YY1 complex promote Z-DNA formation, facilitating the fusion-religation process.","method":"Multi-layer perceptron modeling, imaging strategies in human cancer cells, clinical chip verification, PARP inhibitor functional assays","journal":"Molecular cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple imaging and functional approaches in cancer cells, PARP inhibitor validation; single lab","pmids":["40769147"],"is_preprint":false},{"year":2018,"finding":"M-LPH (Mpv17-like protein) knockout in human hepatoma cells reduces LIG3 protein levels in mitochondria (along with TFAM and OGG1), impairing mitochondrial BER capacity and increasing mtDNA damage. LIG3 protein stability in mitochondria is therefore dependent on M-LPH.","method":"CRISPR-Cas9 M-LPH knockout, Western blot and confocal immunofluorescence of mitochondrial LIG3 protein, mtDNA damage quantification by PCR and 8-OHdG measurement","journal":"Oxidative medicine and cellular longevity","confidence":"Low","confidence_rationale":"Tier 3 / Weak — indirect effect (protein level changes upon KO of another gene), single lab, no direct LIG3 activity assay","pmids":["30310528"],"is_preprint":false},{"year":2025,"finding":"LIG3α binds less frequently to nick substrates (canonical A:T, mismatch G:T, and damaged 8-oxoG:A) than LIG1 but forms longer-lived complexes. Both ligases can bind gap DNA substrates with efficiency comparable to nicks; LIG1 forms more stable long-lived complexes on 1-nucleotide gaps, while LIG3α forms shorter-lived gap complexes. Both discriminate against larger gaps.","method":"Single-molecule total internal reflection fluorescence (TIRF) microscopy; in vitro ligation assays with purified LIG1 and LIG3α on defined substrates","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — single-molecule reconstitution with purified proteins and defined substrates; single preprint, not yet peer-reviewed","pmids":["40666977"],"is_preprint":true},{"year":2025,"finding":"LIG3 associates with telomeres in response to pyridostatin-induced G-quadruplex stabilization and participates in microhomology-mediated end joining (MMEJ) repair at telomeres. Depletion of MMEJ factors (including LIG3) enhances telomere loss in pyridostatin-treated cells.","method":"Telomeric protein composition analysis, MMEJ factor depletion, chemical inhibition, telomere loss assays in human cells treated with pyridostatin","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — telomere association data and depletion with functional readout; single preprint, limited mechanistic detail in abstract","pmids":["41280084"],"is_preprint":true}],"current_model":"LIG3 encodes the sole mitochondrial DNA ligase (essential for mtDNA maintenance and BER) and nuclear DNA ligase IIIα, which forms a complex with XRCC1 for single-strand break repair and BER nick-sealing, participates in alternative NHEJ for DSBs (independently of XRCC1), is recruited to chromatin via PARP1-HPF1-mediated ADP-ribosylation as a backup for Okazaki fragment ligation when LIG1 is absent, and can substitute for LIG4 catalytic activity in NHEJ when LIG4 is present as a structural scaffold; its ligation fidelity at the final BER step is substrate-dependent, with LIG3α unable to seal certain error-free polβ insertion products opposite oxidative lesions."},"narrative":{"mechanistic_narrative":"LIG3 is a DNA ligase that operates in both the mitochondrion and nucleus to seal DNA breaks across multiple repair and replication contexts [PMID:24013086]. As the sole mitochondrial DNA ligase, it is essential for mtDNA maintenance; biallelic loss-of-function variants cause mtDNA depletion and a neurogastrointestinal encephalomyopathy syndrome, with patient cells showing reduced ligase activity and zebrafish lig3 disruption reproducing brain and gut phenotypes [PMID:33855352]. In the nucleus, DNA ligase IIIα partners with XRCC1 to perform nick-sealing in base excision repair and single-strand break repair [PMID:24013086], and serves as a backup for Okazaki fragment ligation when LIG1 is absent: PARP1-HPF1-dependent ADP-ribosylation of histone H3 recruits LIG3 to chromatin for this function [PMID:33872376]. Independently of XRCC1, LIG3 acts in PARP1-dependent alternative end-joining of double-strand breaks, including at telomere-internal breaks [PMID:27806302], and can substitute for LIG4 catalytic activity in NHEJ provided LIG4 is present as a structural scaffold, as shown by the embryonic lethality of combining nuclear LIG3 loss with catalytically inactive LIG4 [PMID:39673806]. LIG3 transcription and its alt-NHEJ activity are amplified in oncogene-driven leukemias through a c-MYC–miRNA axis [PMID:25828893]. Its ligation outcome is substrate-dependent: LIG3α cannot seal certain error-free polβ insertion products opposite 8-oxoG yet ligates the mutagenic alternative, so the choice of ligase determines whether BER ends error-free or mutagenic [PMID:40286853].","teleology":[{"year":2013,"claim":"Establishing that a single gene encodes both the essential mitochondrial DNA ligase and nuclear ligase IIIα defined LIG3 as a multifunctional ligase spanning organellar mtDNA maintenance and several nuclear repair pathways.","evidence":"Review synthesizing KO/knockdown, in vitro ligation, and complementation studies across labs","pmids":["24013086"],"confidence":"High","gaps":["Does not resolve which pathways depend on the XRCC1 partnership versus XRCC1-independent activity in vivo","Relative contribution of LIG3 to alt-NHEJ versus other ligases unquantified"]},{"year":2016,"claim":"Demonstrating PARP1- and LIG3-dependent end-joining of telomere-internal breaks extended LIG3's alt-NHEJ role to a defined genomic context with microhomology signatures.","evidence":"FokI-induced DSBs at telomeres with genetic depletion of PARP1 and LIG3, FISH and microhomology analysis","pmids":["27806302"],"confidence":"Medium","gaps":["Does not establish direct LIG3 recruitment mechanism to telomeric breaks","Overlap with HR pathway at the same lesions not fully separated"]},{"year":2021,"claim":"Identifying PARP1-HPF1-mediated histone H3 ADP-ribosylation as the recruitment signal explained how LIG3-XRCC1 is targeted to chromatin to back up LIG1 in Okazaki fragment ligation.","evidence":"Xenopus egg extract cell-free system with immunodepletion of LIG1/PARP1/HPF1/XRCC1, chromatin fractionation, ADP-ribosylation assays","pmids":["33872376"],"confidence":"High","gaps":["Whether this backup operates in mammalian cells under physiological LIG1 levels untested","Does not address efficiency relative to canonical LIG1 ligation"]},{"year":2021,"claim":"Showing RAD52 antagonizes XRCC1-LIG3α focus formation positioned LIG3-dependent SSBR within a competing pathway choice regulated by ssDNA/PAR-binding factors.","evidence":"XRCC1/LIG3α focus imaging, RAD52 KO/knockdown, camptothecin treatment, ssDNA and PAR binding assays","pmids":["33440161"],"confidence":"Medium","gaps":["Direct physical competition for PAR/ssDNA versus indirect effect not fully resolved","Single lab, imaging-based readout"]},{"year":2021,"claim":"Linking biallelic LIG3 loss-of-function to a mtDNA depletion neurogastrointestinal encephalomyopathy established LIG3 as a Mendelian disease gene and confirmed its non-redundant mitochondrial role in patients and animal models.","evidence":"Whole exome sequencing, patient-cell ligase activity assays, zebrafish lig3 disruption, mtDNA copy number quantification","pmids":["33855352"],"confidence":"High","gaps":["Tissue-specific basis of the neurogastrointestinal phenotype not mechanistically dissected","Does not address whether nuclear LIG3 functions contribute to disease"]},{"year":2015,"claim":"Defining a c-MYC–miR-150/miR-22 axis that upregulates LIG3 and PARP1 connected LIG3-driven alt-NHEJ to genomic instability in oncogene-driven leukemias.","evidence":"c-MYC inhibition, miRNA overexpression, expression analysis in primary/cultured leukemia cells and patient samples, alt-NHEJ assays","pmids":["25828893"],"confidence":"Medium","gaps":["Direct miRNA-LIG3 transcript targeting versus indirect regulation not fully separated","Therapeutic exploitability untested"]},{"year":2018,"claim":"Co-immunoprecipitation of MALAT1 lncRNA with PARP1 and LIG3 suggested an RNA scaffold within the alt-NHEJ complex in multiple myeloma.","evidence":"MALAT1-PARP1/LIG3 RNA-protein co-IP, antisense gapmer knockdown, xenograft functional assays","pmids":["29632340"],"confidence":"Medium","gaps":["Direct versus bridged RNA-protein contacts not resolved","Generality beyond multiple myeloma unknown"]},{"year":2025,"claim":"Mouse genetic epistasis revealed that LIG3 substitutes for LIG4 catalytic activity in NHEJ only when LIG4 remains present as a structural scaffold, clarifying the functional interdependence of the two ligases.","evidence":"Nuclear Lig3 KO crossed to catalytic-dead Lig4 knock-in mice, embryo resorption and lymphocyte development analysis","pmids":["39673806"],"confidence":"High","gaps":["Molecular basis of LIG3 recruitment to the LIG4 scaffold unresolved","Does not identify which NHEJ steps require the scaffold"]},{"year":2025,"claim":"In vitro substrate-specific ligation assays showed LIG3α cannot seal error-free polβ dCTP:8-oxoG products but seals the mutagenic dATP product, establishing the ligase identity as a determinant of BER fidelity.","evidence":"In vitro ligation with purified LIG1 and LIG3α on defined polβ-insertion nick substrates opposite 8-oxoG","pmids":["40286853"],"confidence":"Medium","gaps":["Cellular consequence of this discrimination not demonstrated","Structural basis of the substrate block unknown"]},{"year":2025,"claim":"Single-molecule kinetic comparison distinguished LIG3α from LIG1 by binding frequency and complex lifetime on nick and gap substrates, refining the biophysical basis of their division of labor.","evidence":"Single-molecule TIRF microscopy and in vitro ligation with purified LIG1/LIG3α on defined substrates (preprint)","pmids":["40666977"],"confidence":"Medium","gaps":["Preprint, not yet peer-reviewed","Behavior in the context of partner proteins (XRCC1) not tested"]},{"year":2025,"claim":"A YY1-Lig3-PARP1 complex was implicated in extrachromosomal DNA biogenesis via Lig3-catalyzed religation after YY1-mediated DNA looping, extending LIG3 ligation into a cancer genome-remodeling role.","evidence":"Modeling, imaging in cancer cells, clinical chip verification, PARP inhibitor functional assays","pmids":["40769147"],"confidence":"Medium","gaps":["Direct Lig3-YY1 physical interaction versus complex co-occurrence not fully resolved","Z-DNA/acidic microenvironment mechanism mechanistically incomplete"]},{"year":2025,"claim":"Genetic disruption of FEN1/JMJD1B-dependent flap processing revealed a PARP1-dependent LIG3 alternative Okazaki fragment maturation route that ligates unprocessed flaps at the cost of duplications.","evidence":"JMJD1B disruption, FEN1 R192Q mutation, PARP1 inhibition, PCNA binding and mutagenesis/sequencing (preprint)","pmids":["41280084"],"confidence":"Medium","gaps":["Preprint, not yet peer-reviewed","Frequency of this route under unperturbed replication unknown"]},{"year":null,"claim":"How LIG3 is mechanistically recruited and selected over LIG1/LIG4 in each context, and the structural basis of its substrate-specific ligation outcomes, remains unresolved.","evidence":"No single study in the corpus integrates recruitment, partner selection, and catalytic fidelity","pmids":[],"confidence":"Medium","gaps":["No structural model linking substrate identity to ligation discrimination","Recruitment hierarchy across competing pathways not unified","Tissue-specific contributions of nuclear versus mitochondrial LIG3 unclear"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,6,8,10,13]},{"term_id":"GO:0140097","term_label":"catalytic activity, acting on DNA","supporting_discovery_ids":[0,10]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[13,10]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,6]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,8]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[0,8,5]},{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[1,9]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[1]}],"complexes":["XRCC1-LIG3 complex","PARP1-LIG3 alt-NHEJ complex","YY1-Lig3-PARP1 complex"],"partners":["XRCC1","PARP1","HPF1","LIG4","YY1","MALAT1","RAD52"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P49916","full_name":"DNA ligase 3","aliases":["DNA ligase III","Polydeoxyribonucleotide synthase [ATP] 3"],"length_aa":1009,"mass_kda":112.9,"function":"Isoform 3 functions as a heterodimer with DNA-repair protein XRCC1 in the nucleus and can correct defective DNA strand-break repair and sister chromatid exchange following treatment with ionizing radiation and alkylating agents. Isoform 1 is targeted to mitochondria, where it functions as a DNA ligase in mitochondrial base-excision DNA repair (PubMed:10207110, PubMed:24674627)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/P49916/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/LIG3","classification":"Not Classified","n_dependent_lines":164,"n_total_lines":1208,"dependency_fraction":0.1357615894039735},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"H1F0","stoichiometry":0.2},{"gene":"H2AFZ","stoichiometry":0.2},{"gene":"HIST2H2BE","stoichiometry":0.2},{"gene":"HMGA1","stoichiometry":0.2},{"gene":"HMGN5","stoichiometry":0.2},{"gene":"NUCKS1","stoichiometry":0.2},{"gene":"NUMA1","stoichiometry":0.2},{"gene":"PARP1","stoichiometry":0.2},{"gene":"SSRP1","stoichiometry":0.2},{"gene":"TDP1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/LIG3","total_profiled":1310},"omim":[{"mim_id":"619780","title":"MITOCHONDRIAL DNA DEPLETION SYNDROME 20 (MNGIE TYPE); MTDPS20","url":"https://www.omim.org/entry/619780"},{"mim_id":"618100","title":"MPV17 MITOCHONDRIAL INNER MEMBRANE PROTEIN-LIKE; MPV17L","url":"https://www.omim.org/entry/618100"},{"mim_id":"611035","title":"APRATAXIN- AND PNKP-LIKE FACTOR; APLF","url":"https://www.omim.org/entry/611035"},{"mim_id":"608870","title":"LEUCINE-RICH REPEATS- AND IMMUNOGLOBULIN-LIKE DOMAINS-CONTAINING PROTEIN 3; LRIG3","url":"https://www.omim.org/entry/608870"},{"mim_id":"607207","title":"STIP1 HOMOLOGOUS AND U BOX-CONTAINING PROTEIN 1; STUB1","url":"https://www.omim.org/entry/607207"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/LIG3"},"hgnc":{"alias_symbol":["LIG3alpha"],"prev_symbol":["LIG2"]},"alphafold":{"accession":"P49916","domains":[{"cath_id":"3.30.1740.10","chopping":"94-184","consensus_level":"high","plddt":82.7391,"start":94,"end":184},{"cath_id":"1.10.3260.10","chopping":"255-433","consensus_level":"high","plddt":93.6885,"start":255,"end":433},{"cath_id":"3.30.470.30","chopping":"487-682","consensus_level":"high","plddt":90.5359,"start":487,"end":682},{"cath_id":"2.40.50.140","chopping":"688-835","consensus_level":"high","plddt":91.3343,"start":688,"end":835},{"cath_id":"3.40.50.10190","chopping":"943-1003","consensus_level":"high","plddt":86.9516,"start":943,"end":1003}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P49916","model_url":"https://alphafold.ebi.ac.uk/files/AF-P49916-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P49916-F1-predicted_aligned_error_v6.png","plddt_mean":75.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=LIG3","jax_strain_url":"https://www.jax.org/strain/search?query=LIG3"},"sequence":{"accession":"P49916","fasta_url":"https://rest.uniprot.org/uniprotkb/P49916.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P49916/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P49916"}},"corpus_meta":[{"pmid":"29632340","id":"PMC_29632340","title":"Targeting the MALAT1/PARP1/LIG3 complex induces DNA damage and apoptosis in multiple myeloma.","date":"2018","source":"Leukemia","url":"https://pubmed.ncbi.nlm.nih.gov/29632340","citation_count":130,"is_preprint":false},{"pmid":"27806302","id":"PMC_27806302","title":"Telomere-Internal Double-Strand Breaks Are Repaired by Homologous Recombination and PARP1/Lig3-Dependent End-Joining.","date":"2016","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/27806302","citation_count":88,"is_preprint":false},{"pmid":"25828893","id":"PMC_25828893","title":"c-MYC Generates Repair Errors via Increased Transcription of Alternative-NHEJ Factors, LIG3 and PARP1, in Tyrosine Kinase-Activated Leukemias.","date":"2015","source":"Molecular cancer research : MCR","url":"https://pubmed.ncbi.nlm.nih.gov/25828893","citation_count":57,"is_preprint":false},{"pmid":"24013086","id":"PMC_24013086","title":"Structure and function of the DNA ligases encoded by the mammalian LIG3 gene.","date":"2013","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/24013086","citation_count":54,"is_preprint":false},{"pmid":"33872376","id":"PMC_33872376","title":"HPF1-dependent PARP activation promotes LIG3-XRCC1-mediated backup pathway of Okazaki fragment ligation.","date":"2021","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/33872376","citation_count":48,"is_preprint":false},{"pmid":"33855352","id":"PMC_33855352","title":"Biallelic variants in LIG3 cause a novel mitochondrial neurogastrointestinal encephalomyopathy.","date":"2021","source":"Brain : a journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/33855352","citation_count":39,"is_preprint":false},{"pmid":"37315345","id":"PMC_37315345","title":"CircRNA Galntl6 sponges miR-335 to ameliorate stress-induced hypertension through upregulating Lig3 in rostral ventrolateral medulla.","date":"2023","source":"Redox 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journal of the European Society for Therapeutic Radiology and Oncology","url":"https://pubmed.ncbi.nlm.nih.gov/21620500","citation_count":16,"is_preprint":false},{"pmid":"25817347","id":"PMC_25817347","title":"Polymorphism of the LIG3 gene in keratoconus and Fuchs endothelial corneal dystrophy.","date":"2015","source":"Cellular and molecular biology (Noisy-le-Grand, France)","url":"https://pubmed.ncbi.nlm.nih.gov/25817347","citation_count":12,"is_preprint":false},{"pmid":"33440161","id":"PMC_33440161","title":"RAD52 Adjusts Repair of Single-Strand Breaks via Reducing DNA-Damage-Promoted XRCC1/LIG3α Co-localization.","date":"2021","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/33440161","citation_count":12,"is_preprint":false},{"pmid":"40769147","id":"PMC_40769147","title":"Extrachromosomal DNA biogenesis is dependent on DNA looping and religation by YY1-Lig3-PARylation complex.","date":"2025","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/40769147","citation_count":8,"is_preprint":false},{"pmid":"30310528","id":"PMC_30310528","title":"Knockout of Mpv17-Like Protein (M-LPH) Gene in Human Hepatoma Cells Results in Impairment of mtDNA Integrity through Reduction of TFAM, OGG1, and LIG3 at the Protein Levels.","date":"2018","source":"Oxidative medicine and cellular longevity","url":"https://pubmed.ncbi.nlm.nih.gov/30310528","citation_count":6,"is_preprint":false},{"pmid":"31034940","id":"PMC_31034940","title":"LIG3 gene polymorphisms and risk of gastric cancer in a Southern Chinese population.","date":"2019","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/31034940","citation_count":5,"is_preprint":false},{"pmid":"39673806","id":"PMC_39673806","title":"Lig3-dependent rescue of mouse viability and DNA double-strand break repair by catalytically inactive Lig4.","date":"2025","source":"Nucleic acids 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Part A","url":"https://pubmed.ncbi.nlm.nih.gov/41741356","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.08.13.670189","title":"The interplay between glucose and aromatic compound regulation by two IclR-type transcription factors, LigR1 and LigR2, in  <i>Pseudomonas putida</i>  KT2440","date":"2025-08-13","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.13.670189","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.11.25.690390","title":"Rescue from pyridostatin-stabilized telomeric G-quadruplexes by DNA cleavage and microhomology-mediated end joining","date":"2025-11-30","source":"bioRxiv","url":"https://doi.org/10.1101/2025.11.25.690390","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.08.24.672030","title":"GCN5-TADA2B in the SAGA complex provide constitutive fine-tuning control of XRCC1 recruitment and focal retention at DNA damage sites","date":"2025-08-28","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.24.672030","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.02.15.638465","title":"Single Cell Proteomics Reveals Novel Cell Phenotypes in Marfan Mouse Aneurysm","date":"2025-02-23","source":"bioRxiv","url":"https://doi.org/10.1101/2025.02.15.638465","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":16662,"output_tokens":3878,"usd":0.054078,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11663,"output_tokens":4305,"usd":0.08297,"stage2_stop_reason":"end_turn"},"total_usd":0.137048,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2013,\n      \"finding\": \"The LIG3 gene encodes multiple DNA ligase polypeptides: the only mitochondrial DNA ligase (essential for that organelle), and nuclear DNA ligase IIIα which partners with XRCC1 in base excision repair (BER) and single-strand break repair. Nuclear LIG3α also functions in an alternative NHEJ (alt-NHEJ) pathway for DSB repair that is independent of its XRCC1 interaction, and can substitute for LIG1 in DNA replication when LIG1 is absent.\",\n      \"method\": \"Review synthesizing genetic, biochemical, and cell biological experiments across multiple studies\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal experimental approaches replicated across labs, including KO/knockdown, in vitro assays, and complementation studies\",\n      \"pmids\": [\"24013086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"LIG3-XRCC1 complex serves as a backup system for Okazaki fragment ligation when LIG1 is absent. PARP1-HPF1-dependent ADP-ribosylation of histone H3 is required to recruit LIG3 onto chromatin for this backup ligation; depletion of PARP1 or HPF1 prevents LIG3 chromatin recruitment and Okazaki fragment joining in the absence of LIG1.\",\n      \"method\": \"Cell-free system from Xenopus egg extracts with immunodepletion of LIG1, PARP1, HPF1, and XRCC1; chromatin fractionation; ADP-ribosylation assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — reconstitution in cell-free system with multiple depletions and orthogonal biochemical readouts in a single rigorous study\",\n      \"pmids\": [\"33872376\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"RAD52 inhibits single-strand break repair (SSBR) by reducing DNA-damage-promoted co-localization of XRCC1 and LIG3α at repair foci, via RAD52's high-affinity binding to single-stranded DNA (ssDNA) and poly(ADP-ribose) (PAR).\",\n      \"method\": \"Co-localization/imaging of XRCC1/LIG3α foci, RAD52 knockout/knockdown, camptothecin treatment, ssDNA and PAR binding assays, cell survival assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (imaging, binding assays, KO) in a single lab\",\n      \"pmids\": [\"33440161\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"MALAT1 lncRNA physically binds PARP1 and LIG3 and is a component of the alternative NHEJ (A-NHEJ) protein complex in multiple myeloma cells; degradation of MALAT1 by antisense oligonucleotides disrupts this complex, increases poly-ADP-ribosylation of nuclear proteins, and defects the DNA repair pathway leading to apoptosis.\",\n      \"method\": \"RNA-protein binding (co-immunoprecipitation of MALAT1 with PARP1/LIG3), antisense gapmer knockdown, in vitro and in vivo (xenograft) functional assays\",\n      \"journal\": \"Leukemia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — RNA-protein pulldown combined with functional knockdown and in vivo validation; single lab\",\n      \"pmids\": [\"29632340\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"c-MYC transcriptionally activates LIG3 and PARP1 expression in BCR-ABL1- and FLT3/ITD-driven leukemias. c-MYC negatively regulates miR-150 and miR-22, which in turn suppress LIG3 and PARP1, driving increased alt-NHEJ activity and genomic instability.\",\n      \"method\": \"c-MYC inhibition, miRNA overexpression (miR-150, miR-22), gene expression analysis in primary and cultured leukemia cells and patient samples, alt-NHEJ activity assays\",\n      \"journal\": \"Molecular cancer research : MCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple complementary approaches (inhibitor, miRNA OE, patient samples) in a single lab\",\n      \"pmids\": [\"25828893\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Telomere-internal double-strand breaks are repaired by a PARP1- and LIG3-dependent end-joining reaction consistent with alt-NHEJ or single-strand break repair, in addition to homologous recombination.\",\n      \"method\": \"FokI-induced DSBs at telomeres, genetic depletion of PARP1 and LIG3, telomere FISH and imaging, microhomology analysis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic depletion with specific functional readout (telomere repair), single lab\",\n      \"pmids\": [\"27806302\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Biallelic loss-of-function variants in LIG3 cause mitochondrial DNA depletion (without multiple deletions), impair mtDNA maintenance, and result in mitochondrial dysfunction manifesting as a neurogastrointestinal encephalomyopathy syndrome. Patient-derived cells show reduced LIG3 protein and ligase activity; disruption of lig3 in zebrafish reproduces brain alterations and gut transit impairment.\",\n      \"method\": \"Whole exome sequencing, in vitro ligase activity assays in patient cells, zebrafish lig3 disruption model, mtDNA copy number quantification, muscle biopsy/COX staining\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro functional assays, multiple patient families, zebrafish model replication; multiple orthogonal methods\",\n      \"pmids\": [\"33855352\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Sirt3 deacetylates LIG3 protein (along with other BER enzymes NEIL1, NEIL2, OGG1, MUTYH, APE1) in mitochondria; LIG3 is a substrate for Sirt3-mediated deacetylation, which modulates LIG3 activity in the mitochondrial BER pathway.\",\n      \"method\": \"Deacetylation assay with Sirt3 and BER substrates including LIG3 in colorectal cancer cells\",\n      \"journal\": \"Polski przeglad chirurgiczny\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single enzymatic assay, single lab, limited methodological detail in abstract\",\n      \"pmids\": [\"32312920\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Nuclear LIG3 is recruited to NHEJ complexes to facilitate end joining in the presence (but not catalytic activity) of LIG4. Mice lacking nuclear LIG3 and expressing catalytically inactive LIG4 die as embryos (lethal genetic interaction), whereas nuclear LIG3-deficient mice alone are viable, demonstrating that LIG3 substitutes for LIG4 catalytic activity in NHEJ when LIG4 is present as a structural scaffold.\",\n      \"method\": \"Mouse genetics: nuclear Lig3 knockout strain crossed to Lig4 catalytic-dead knock-in; timed mating/embryo resorption analysis; lymphocyte development assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic epistasis with two independent mouse strains, embryonic lethality as definitive readout, rigorous genetic interaction\",\n      \"pmids\": [\"39673806\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LIG3 (with PARP1) performs an alternative Okazaki fragment maturation (OFM) process: when FEN1 demethylation by JMJD1B and subsequent LIG1 recruitment is disrupted, unprocessed 5' flaps trigger PARP1-dependent LIG3 recruitment to join incompletely processed Okazaki fragments. LIG3 has flap ligation activity in this context, supporting cell survival but causing duplications and mutations.\",\n      \"method\": \"Cell-based genetic disruption of JMJD1B and FEN1 R192Q mutation; PARP1 inhibition; PCNA binding assays; mutagenesis/sequencing\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple genetic and biochemical approaches in single preprint lab; not yet peer-reviewed\",\n      \"pmids\": [\"41280084\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LIG3α exhibits an inability to ligate polβ dCTP:8-oxoG insertion products (error-free repair intermediates) at the final BER step, while it can seal nicks from polβ mutagenic dATP insertion opposite 8-oxoG. This demonstrates that the identity of the BER ligase critically determines repair outcome (mutagenic vs. error-free) at the ligation step.\",\n      \"method\": \"In vitro ligation assays with purified LIG1 and LIG3α on defined nick substrates containing polβ insertion products opposite 8-oxoG\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstitution with defined substrates, single lab, single study\",\n      \"pmids\": [\"40286853\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"YY1-Lig3-PARP1 form a complex in which Lig3 catalyzes DNA religation after YY1-mediated DNA looping to drive extrachromosomal DNA (ecDNA) biogenesis. PARylation-dependent acidic microenvironments mediated by the Lig3-YY1 complex promote Z-DNA formation, facilitating the fusion-religation process.\",\n      \"method\": \"Multi-layer perceptron modeling, imaging strategies in human cancer cells, clinical chip verification, PARP inhibitor functional assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple imaging and functional approaches in cancer cells, PARP inhibitor validation; single lab\",\n      \"pmids\": [\"40769147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"M-LPH (Mpv17-like protein) knockout in human hepatoma cells reduces LIG3 protein levels in mitochondria (along with TFAM and OGG1), impairing mitochondrial BER capacity and increasing mtDNA damage. LIG3 protein stability in mitochondria is therefore dependent on M-LPH.\",\n      \"method\": \"CRISPR-Cas9 M-LPH knockout, Western blot and confocal immunofluorescence of mitochondrial LIG3 protein, mtDNA damage quantification by PCR and 8-OHdG measurement\",\n      \"journal\": \"Oxidative medicine and cellular longevity\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — indirect effect (protein level changes upon KO of another gene), single lab, no direct LIG3 activity assay\",\n      \"pmids\": [\"30310528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LIG3α binds less frequently to nick substrates (canonical A:T, mismatch G:T, and damaged 8-oxoG:A) than LIG1 but forms longer-lived complexes. Both ligases can bind gap DNA substrates with efficiency comparable to nicks; LIG1 forms more stable long-lived complexes on 1-nucleotide gaps, while LIG3α forms shorter-lived gap complexes. Both discriminate against larger gaps.\",\n      \"method\": \"Single-molecule total internal reflection fluorescence (TIRF) microscopy; in vitro ligation assays with purified LIG1 and LIG3α on defined substrates\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — single-molecule reconstitution with purified proteins and defined substrates; single preprint, not yet peer-reviewed\",\n      \"pmids\": [\"40666977\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LIG3 associates with telomeres in response to pyridostatin-induced G-quadruplex stabilization and participates in microhomology-mediated end joining (MMEJ) repair at telomeres. Depletion of MMEJ factors (including LIG3) enhances telomere loss in pyridostatin-treated cells.\",\n      \"method\": \"Telomeric protein composition analysis, MMEJ factor depletion, chemical inhibition, telomere loss assays in human cells treated with pyridostatin\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — telomere association data and depletion with functional readout; single preprint, limited mechanistic detail in abstract\",\n      \"pmids\": [\"41280084\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"LIG3 encodes the sole mitochondrial DNA ligase (essential for mtDNA maintenance and BER) and nuclear DNA ligase IIIα, which forms a complex with XRCC1 for single-strand break repair and BER nick-sealing, participates in alternative NHEJ for DSBs (independently of XRCC1), is recruited to chromatin via PARP1-HPF1-mediated ADP-ribosylation as a backup for Okazaki fragment ligation when LIG1 is absent, and can substitute for LIG4 catalytic activity in NHEJ when LIG4 is present as a structural scaffold; its ligation fidelity at the final BER step is substrate-dependent, with LIG3α unable to seal certain error-free polβ insertion products opposite oxidative lesions.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"LIG3 is a DNA ligase that operates in both the mitochondrion and nucleus to seal DNA breaks across multiple repair and replication contexts [#0]. As the sole mitochondrial DNA ligase, it is essential for mtDNA maintenance; biallelic loss-of-function variants cause mtDNA depletion and a neurogastrointestinal encephalomyopathy syndrome, with patient cells showing reduced ligase activity and zebrafish lig3 disruption reproducing brain and gut phenotypes [#6]. In the nucleus, DNA ligase IIIα partners with XRCC1 to perform nick-sealing in base excision repair and single-strand break repair [#0], and serves as a backup for Okazaki fragment ligation when LIG1 is absent: PARP1-HPF1-dependent ADP-ribosylation of histone H3 recruits LIG3 to chromatin for this function [#1]. Independently of XRCC1, LIG3 acts in PARP1-dependent alternative end-joining of double-strand breaks, including at telomere-internal breaks [#5], and can substitute for LIG4 catalytic activity in NHEJ provided LIG4 is present as a structural scaffold, as shown by the embryonic lethality of combining nuclear LIG3 loss with catalytically inactive LIG4 [#8]. LIG3 transcription and its alt-NHEJ activity are amplified in oncogene-driven leukemias through a c-MYC–miRNA axis [#4]. Its ligation outcome is substrate-dependent: LIG3α cannot seal certain error-free polβ insertion products opposite 8-oxoG yet ligates the mutagenic alternative, so the choice of ligase determines whether BER ends error-free or mutagenic [#10].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Establishing that a single gene encodes both the essential mitochondrial DNA ligase and nuclear ligase IIIα defined LIG3 as a multifunctional ligase spanning organellar mtDNA maintenance and several nuclear repair pathways.\",\n      \"evidence\": \"Review synthesizing KO/knockdown, in vitro ligation, and complementation studies across labs\",\n      \"pmids\": [\"24013086\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not resolve which pathways depend on the XRCC1 partnership versus XRCC1-independent activity in vivo\", \"Relative contribution of LIG3 to alt-NHEJ versus other ligases unquantified\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrating PARP1- and LIG3-dependent end-joining of telomere-internal breaks extended LIG3's alt-NHEJ role to a defined genomic context with microhomology signatures.\",\n      \"evidence\": \"FokI-induced DSBs at telomeres with genetic depletion of PARP1 and LIG3, FISH and microhomology analysis\",\n      \"pmids\": [\"27806302\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not establish direct LIG3 recruitment mechanism to telomeric breaks\", \"Overlap with HR pathway at the same lesions not fully separated\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identifying PARP1-HPF1-mediated histone H3 ADP-ribosylation as the recruitment signal explained how LIG3-XRCC1 is targeted to chromatin to back up LIG1 in Okazaki fragment ligation.\",\n      \"evidence\": \"Xenopus egg extract cell-free system with immunodepletion of LIG1/PARP1/HPF1/XRCC1, chromatin fractionation, ADP-ribosylation assays\",\n      \"pmids\": [\"33872376\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this backup operates in mammalian cells under physiological LIG1 levels untested\", \"Does not address efficiency relative to canonical LIG1 ligation\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showing RAD52 antagonizes XRCC1-LIG3α focus formation positioned LIG3-dependent SSBR within a competing pathway choice regulated by ssDNA/PAR-binding factors.\",\n      \"evidence\": \"XRCC1/LIG3α focus imaging, RAD52 KO/knockdown, camptothecin treatment, ssDNA and PAR binding assays\",\n      \"pmids\": [\"33440161\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct physical competition for PAR/ssDNA versus indirect effect not fully resolved\", \"Single lab, imaging-based readout\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linking biallelic LIG3 loss-of-function to a mtDNA depletion neurogastrointestinal encephalomyopathy established LIG3 as a Mendelian disease gene and confirmed its non-redundant mitochondrial role in patients and animal models.\",\n      \"evidence\": \"Whole exome sequencing, patient-cell ligase activity assays, zebrafish lig3 disruption, mtDNA copy number quantification\",\n      \"pmids\": [\"33855352\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-specific basis of the neurogastrointestinal phenotype not mechanistically dissected\", \"Does not address whether nuclear LIG3 functions contribute to disease\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defining a c-MYC–miR-150/miR-22 axis that upregulates LIG3 and PARP1 connected LIG3-driven alt-NHEJ to genomic instability in oncogene-driven leukemias.\",\n      \"evidence\": \"c-MYC inhibition, miRNA overexpression, expression analysis in primary/cultured leukemia cells and patient samples, alt-NHEJ assays\",\n      \"pmids\": [\"25828893\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct miRNA-LIG3 transcript targeting versus indirect regulation not fully separated\", \"Therapeutic exploitability untested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Co-immunoprecipitation of MALAT1 lncRNA with PARP1 and LIG3 suggested an RNA scaffold within the alt-NHEJ complex in multiple myeloma.\",\n      \"evidence\": \"MALAT1-PARP1/LIG3 RNA-protein co-IP, antisense gapmer knockdown, xenograft functional assays\",\n      \"pmids\": [\"29632340\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus bridged RNA-protein contacts not resolved\", \"Generality beyond multiple myeloma unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Mouse genetic epistasis revealed that LIG3 substitutes for LIG4 catalytic activity in NHEJ only when LIG4 remains present as a structural scaffold, clarifying the functional interdependence of the two ligases.\",\n      \"evidence\": \"Nuclear Lig3 KO crossed to catalytic-dead Lig4 knock-in mice, embryo resorption and lymphocyte development analysis\",\n      \"pmids\": [\"39673806\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of LIG3 recruitment to the LIG4 scaffold unresolved\", \"Does not identify which NHEJ steps require the scaffold\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"In vitro substrate-specific ligation assays showed LIG3α cannot seal error-free polβ dCTP:8-oxoG products but seals the mutagenic dATP product, establishing the ligase identity as a determinant of BER fidelity.\",\n      \"evidence\": \"In vitro ligation with purified LIG1 and LIG3α on defined polβ-insertion nick substrates opposite 8-oxoG\",\n      \"pmids\": [\"40286853\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cellular consequence of this discrimination not demonstrated\", \"Structural basis of the substrate block unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Single-molecule kinetic comparison distinguished LIG3α from LIG1 by binding frequency and complex lifetime on nick and gap substrates, refining the biophysical basis of their division of labor.\",\n      \"evidence\": \"Single-molecule TIRF microscopy and in vitro ligation with purified LIG1/LIG3α on defined substrates (preprint)\",\n      \"pmids\": [\"40666977\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not yet peer-reviewed\", \"Behavior in the context of partner proteins (XRCC1) not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A YY1-Lig3-PARP1 complex was implicated in extrachromosomal DNA biogenesis via Lig3-catalyzed religation after YY1-mediated DNA looping, extending LIG3 ligation into a cancer genome-remodeling role.\",\n      \"evidence\": \"Modeling, imaging in cancer cells, clinical chip verification, PARP inhibitor functional assays\",\n      \"pmids\": [\"40769147\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct Lig3-YY1 physical interaction versus complex co-occurrence not fully resolved\", \"Z-DNA/acidic microenvironment mechanism mechanistically incomplete\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Genetic disruption of FEN1/JMJD1B-dependent flap processing revealed a PARP1-dependent LIG3 alternative Okazaki fragment maturation route that ligates unprocessed flaps at the cost of duplications.\",\n      \"evidence\": \"JMJD1B disruption, FEN1 R192Q mutation, PARP1 inhibition, PCNA binding and mutagenesis/sequencing (preprint)\",\n      \"pmids\": [\"41280084\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not yet peer-reviewed\", \"Frequency of this route under unperturbed replication unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How LIG3 is mechanistically recruited and selected over LIG1/LIG4 in each context, and the structural basis of its substrate-specific ligation outcomes, remains unresolved.\",\n      \"evidence\": \"No single study in the corpus integrates recruitment, partner selection, and catalytic fidelity\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model linking substrate identity to ligation discrimination\", \"Recruitment hierarchy across competing pathways not unified\", \"Tissue-specific contributions of nuclear versus mitochondrial LIG3 unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 6, 8, 10, 13]},\n      {\"term_id\": \"GO:0140097\", \"supporting_discovery_ids\": [0, 10]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [13, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 8]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [0, 8, 5]},\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [1, 9]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [\n      \"XRCC1-LIG3 complex\",\n      \"PARP1-LIG3 alt-NHEJ complex\",\n      \"YY1-Lig3-PARP1 complex\"\n    ],\n    \"partners\": [\n      \"XRCC1\",\n      \"PARP1\",\n      \"HPF1\",\n      \"LIG4\",\n      \"YY1\",\n      \"MALAT1\",\n      \"RAD52\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":6,"faith_total":6,"faith_pct":100.0}}