{"gene":"RAD50","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":1996,"finding":"Human RAD50 protein is stably associated with human MRE11 in a protein complex, identified as the human homolog of yeast Rad50 which functions in a multiprotein complex analogous to the yeast Rad50/Mre11/Xrs2 complex.","method":"Co-immunoprecipitation, cDNA isolation and characterization","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP establishing complex, replicated across multiple subsequent studies","pmids":["8756642"],"is_preprint":false},{"year":1997,"finding":"hMRE11 and hRAD50 form discrete nuclear foci in response to DNA double-strand break-inducing agents (ionizing radiation) but not UV irradiation, and focus formation is markedly reduced in ataxia-telangiectasia cells, indicating dependence on a DNA damage-induced signaling pathway.","method":"Immunofluorescence, cell irradiation experiments","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct localization experiment with functional consequence, replicated across labs","pmids":["9315668"],"is_preprint":false},{"year":1998,"finding":"The hMRE11/hRAD50 complex includes a third component, p95/NBS1 (the gene mutated in Nijmegen breakage syndrome); p95 deficiency abrogates formation of hMRE11/hRAD50 ionizing radiation-induced foci, linking DSB repair to cell cycle checkpoint functions.","method":"Gene mapping, immunofluorescence, cell biology in NBS patient-derived cells","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods, replicated across labs, foundational complex identification","pmids":["9590181"],"is_preprint":false},{"year":1999,"finding":"BRCA1 interacts in vitro and in vivo with hRAD50 (which forms a complex with hMRE11 and p95/nibrin); upon irradiation, BRCA1 co-localizes with hRAD50 in nuclear foci, and wild-type BRCA1 is required for formation of these foci and for cellular resistance to DNA damage.","method":"In vitro binding assay, co-immunoprecipitation, immunofluorescence colocalization","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP plus in vitro binding plus functional rescue experiment","pmids":["10426999"],"is_preprint":false},{"year":1999,"finding":"The triple complex of recombinant NBS1, MRE11, and RAD50 displays ATP-stimulated DNA unwinding and efficient cleavage of fully paired hairpins not seen with MRE11/RAD50 alone; RAD50 is responsible for ATP binding by the complex, and ATP controls a switch in endonuclease specificity allowing cleavage of 3'-protruding strands at double-/single-strand transitions.","method":"Biochemical reconstitution with recombinant proteins, mutational analysis, in vitro nuclease/helicase assays","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution with purified recombinant proteins and mutagenesis, replicated by multiple labs","pmids":["10346816"],"is_preprint":false},{"year":2000,"finding":"A small fraction of RAD50, MRE11, and NBS1 is associated with TRF2 immunocomplexes; RAD50 and MRE11 localize to interphase telomeres, and NBS1 associates with TRF2 and telomeres specifically in S phase but not G1 or G2, indicating cell-cycle-regulated association of MRN with telomeres.","method":"Nanoelectrospray tandem mass spectrometry, protein blotting, indirect immunofluorescence","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — mass spectrometry identification plus immunofluorescence localization, replicated across multiple subsequent studies","pmids":["10888888"],"is_preprint":false},{"year":2001,"finding":"Crystal structures of Pyrococcus furiosus Mre11 reveal a protein phosphatase-like dimanganese-binding nuclease domain; the structure of P. furiosus Rad50 ABC-ATPase with adjacent coiled-coil defines a compact Mre11/Rad50-ATPase complex and suggests that Rad50 ATP-driven conformational switching directly controls the Mre11 exonuclease; the MR complex exists as a (Mre11)2/(Rad50)2 heterotetrameric DNA-processing head with a double coiled-coil linker.","method":"X-ray crystallography, electron microscopy, small-angle X-ray scattering, ultracentrifugation","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures with multiple orthogonal structural methods and functional mapping","pmids":["11371344"],"is_preprint":false},{"year":2001,"finding":"Purified yeast Rad50 and Mre11 form a stable equimolar complex. Mre11 has 3'→5' exonuclease activity releasing mononucleotides; addition of Rad50 does not significantly alter this exonuclease activity. Mre11 has endonuclease activity on hairpins and 3' ssDNA tails, and these endonuclease activities are markedly enhanced by Rad50 only in the presence of ATP.","method":"Protein purification, in vitro nuclease assays, ATP-dependence studies","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro biochemical reconstitution with purified proteins, multiple substrates tested","pmids":["11454871"],"is_preprint":false},{"year":2001,"finding":"NBS1 C-terminal sequence (residues 665-693) is essential for hMRE11 binding and is necessary for nuclear localization of the MRE11/RAD50 complex and cellular radiation resistance; the N-terminal FHA domain regulates nuclear foci formation in response to DNA damage but is not essential for nuclear transport or radiation resistance.","method":"Deletion mutagenesis, co-immunoprecipitation, cellular localization experiments, radiation sensitivity assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — structure-function mutagenesis with cellular validation, single lab with multiple orthogonal methods","pmids":["11062235"],"is_preprint":false},{"year":2002,"finding":"The Rad50 coiled-coil region contains a zinc-hook dimer interface where pairs of conserved Cys-X-X-Cys motifs form interlocking hooks that bind one Zn2+ ion; these hooks join oppositely protruding Rad50 coiled-coil domains to form a flexible bridge of up to 1,200 Å, enabling DNA tethering. Mutations in this zinc-hook motif confer radiation sensitivity in yeast and disrupt binding at the distant Mre11 nuclease interface.","method":"X-ray crystallography (2.2 Å), electron microscopy, biochemical assays, yeast genetics","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus EM plus biochemical and genetic validation, multiple orthogonal methods","pmids":["12152085"],"is_preprint":false},{"year":2002,"finding":"Rad50 ATP-binding domains share structural and mechanistic conservation with ABC transporters; ATP binding drives conformational changes in substrate-specific domains, functioning as a chemo-mechanical device in DNA repair.","method":"Structural analysis, comparative crystallography","journal":"Current opinion in structural biology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — structural analysis reviewed, but primarily a synthesis/review perspective without new experimental validation","pmids":["12727520"],"is_preprint":false},{"year":2002,"finding":"Rad50 S793R signature motif mutation prevents ATP binding and disrupts communication among other ATP-binding loops, prevents Rad50 dimerization; the equivalent mutation in human RAD50 forms a complex with MRE11 and NBS1 but is specifically deficient in all ATP-dependent enzymatic activities; the same mutation in S. cerevisiae fails to complement rad50 deletion in DNA repair assays.","method":"X-ray crystallography, biochemical ATPase assays, yeast genetic complementation","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus mutagenesis plus in vitro biochemistry plus in vivo genetic validation","pmids":["14698290"],"is_preprint":false},{"year":2004,"finding":"The MRN complex directly activates ATM kinase activity in vitro toward substrates p53, Chk2, and histone H2AX; MRN makes multiple contacts with ATM and stimulates ATM activity by facilitating stable substrate binding; phosphorylation of NBS1 is critical for MRN stimulation of ATM activity toward Chk2 but not p53.","method":"In vitro kinase assays with recombinant proteins, protein interaction studies","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified recombinant components, multiple substrates and mutants tested","pmids":["15064416"],"is_preprint":false},{"year":2004,"finding":"A novel RAD50-interacting protein, RINT-1, was identified via yeast two-hybrid screening; RINT-1 binds specifically to RAD50 during late S and G2/M phases of the cell cycle; cells expressing truncated RINT-1 display a defective radiation-induced G2/M checkpoint.","method":"Yeast two-hybrid screen, co-immunoprecipitation, cell cycle analysis, checkpoint assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — yeast two-hybrid plus co-IP with functional phenotype, single lab","pmids":["11096100"],"is_preprint":false},{"year":2004,"finding":"RPA and the MRN complex (MRE11, RAD50, NBS1) co-localize to discrete nuclear foci and physically interact in response to DNA replication fork blockage by HU or UV; co-immunoprecipitation of RPA with anti-RAD50 antibody was demonstrated; phosphorylation of both RPA and MRE11 is required for this interaction.","method":"Co-immunoprecipitation, immunofluorescence, subcellular fractionation, phosphatase treatment","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP with multiple antibodies plus fractionation, single lab","pmids":["15180989"],"is_preprint":false},{"year":2005,"finding":"DNA binding by the hRAD50/MRE11/NBS1 globular domain leads to parallel orientation of the coiled coils, preventing intracomplex interactions and favoring intercomplex associations needed for DNA tethering; this conformational change is transmitted 50 nm from the DNA-binding domain to the coiled-coil apices.","method":"Atomic force microscopy, electron microscopy, single-molecule imaging","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct structural/biophysical visualization of conformational change upon DNA binding, single lab with rigorous single-molecule methods","pmids":["16163361"],"is_preprint":false},{"year":2006,"finding":"ATM activation by DSBs occurs in two steps: first, dimeric ATM is recruited to damaged DNA and dissociates into monomers (facilitated by MRN tethering DNA to increase local concentration); second, the ATM-binding domain of NBS1 is required and sufficient to convert unphosphorylated ATM monomers into enzymatically active monomers in the absence of DNA.","method":"Biochemical reconstitution, Xenopus cell-free extract system, mutational analysis","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution in cell-free system with defined mutants, multiple orthogonal approaches","pmids":["16622404"],"is_preprint":false},{"year":2007,"finding":"MRE11-RAD50-NBS1 and ATM function as co-mediators of TRF1 in telomere length control; RAD50 targeted to telomeres downregulates TRF1 association with telomeric DNA; ATM-mediated phosphorylation of TRF1 impairs its ability to bind telomeric DNA in vitro, and MRN is required for this TRF1 phosphorylation by ATM.","method":"Chromatin immunoprecipitation, telomere-targeted overexpression, in vitro DNA binding assays, RNAi knockdown","journal":"Nature structural & molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple methods including in vitro binding and cellular experiments, single lab","pmids":["17694070"],"is_preprint":false},{"year":2007,"finding":"Mre11/Rad50 complexes from three organisms (human, yeast, archaeal) catalyze the reversible adenylate kinase reaction in vitro; mutation of the conserved signature motif reduces adenylate kinase activity without reducing ATP hydrolysis; this mutant resembles a rad50 null strain for meiosis and telomere maintenance; adenylate kinase inhibitor blocks Mre11/Rad50-dependent DNA tethering in vitro and in cell-free extracts.","method":"In vitro enzymatic assays, yeast genetics, pharmacological inhibition, cell-free extract DNA tethering assay","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with multiple organisms, mutagenesis, genetic and chemical validation","pmids":["17349953"],"is_preprint":false},{"year":2009,"finding":"NBS1 FHA domain recruits phosphorylated Ctp1 to DSBs via binding of the NBS1 FHA domain to a Ctp1 pThr-Asp motif; fission yeast and human NBS1 structures reveal fused FHA-BRCT1-BRCT2 domains flexibly linked to C-terminal Mre11- and ATM-binding motifs; Nbs1 tethers Ctp1/CtIP to the immediate vicinity of DSBs to restrict DNA end processing activities.","method":"X-ray crystallography, SAXS, genetic analysis, biochemical binding assays","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures plus SAXS plus genetic and biochemical validation, multiple orthogonal methods","pmids":["19804755"],"is_preprint":false},{"year":2010,"finding":"Biochemical reconstitution of DNA end resection shows that the yeast MRX complex and Sae2 stimulate Exo1-mediated 5' strand degradation through cooperative binding of DNA substrates; MRX recruits Dna2 nuclease to DSB ends and stimulates recruitment of Exo1 while antagonizing excess Ku binding to DSB ends.","method":"In vitro resection reconstitution with purified proteins, ChIP in yeast","journal":"Nature; The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — independent biochemical reconstitutions in two labs (Kowalczykowski and Lee/Ira groups)","pmids":["20811461","20834227"],"is_preprint":false},{"year":2010,"finding":"MRX and Sae2 directly promote 5' strand resection; reconstitution with purified MRX, Sae2, and Exo1 shows that 5' strand degradation is catalyzed by Exo1 yet completely dependent on MRX and Sae2 when Exo1 levels are limiting, mainly through cooperative DNA substrate binding.","method":"In vitro resection reconstitution with purified recombinant proteins","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — biochemical reconstitution with purified components, replicated across labs","pmids":["21102445"],"is_preprint":false},{"year":2011,"finding":"Crystal structure of the Mre11-Rad50-ATPγS complex shows Mre11 promotes ATPase activity of Rad50 by holding the coiled-coil arm and stabilizing the signature motif and P-loop; ATP-bound Rad50 negatively regulates Mre11 nuclease activity by blocking the Mre11 active site; ATP hydrolysis disengages Rad50 molecules and causes conformational change in Mre11's flexible linker to unmask the Mre11 active site.","method":"X-ray crystallography, biochemical ATPase and nuclease assays","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus biochemical validation, multiple orthogonal methods","pmids":["21511873"],"is_preprint":false},{"year":2011,"finding":"ATM phosphorylates RAD50 at Ser-635; a RAD50 S635G phosphosite mutant supports normal ATM activation but is defective in correcting DNA damage-induced signaling through ATM-dependent substrate SMC1, fails to correct radiosensitivity, DSB repair, and S-phase checkpoint defects, without disrupting MRE11/RAD50/NBS1 complex integrity.","method":"Phosphorylation site mapping, site-directed mutagenesis, functional complementation in RAD50-deficient cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — specific phosphosite identified and validated by mutagenesis with multiple functional readouts, single lab","pmids":["21757780"],"is_preprint":false},{"year":2011,"finding":"ATP binding to RAD50 induces a closed conformation in which MRE11 functions as an endonuclease; ATP hydrolysis opens the RAD50-MRE11 complex and MRE11 maintains exonuclease activity. Thus, ATP hydrolysis acts as a molecular switch converting MRE11 from endonuclease to exonuclease.","method":"In vitro nuclease assays, EM visualization of conformational states, ATP binding/hydrolysis studies","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with conformational visualization plus functional nuclease assays, single lab","pmids":["22102415"],"is_preprint":false},{"year":2013,"finding":"MRN complex visualized by single-molecule FRET unwinds 15-20 base pairs at the end of a duplex DNA molecule, holding the branched structure open for minutes in an ATP-dependent reaction; a Rad50 catalytic domain mutant deficient in this ATP-dependent DNA unwinding is impaired in DNA end resection in vitro and in resection-dependent repair in human cells.","method":"Single-molecule FRET, in vitro resection assays, human cell DNA repair assays","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 1 / Moderate — single-molecule biophysics plus mutagenesis plus cellular validation, multiple orthogonal methods","pmids":["24191051"],"is_preprint":false},{"year":2014,"finding":"RAD50 interacts directly with innate immune adaptor CARD9 in the cytoplasm; dsDNA induces formation of dsDNA-RAD50-CARD9 signaling complexes activating NF-κB and generating pro-IL-1β; cells conditionally deficient in RAD50 exhibit defective DNA-induced IL-1β production.","method":"Co-immunoprecipitation, conditional knockout cells, cytokine assays, in vivo infection model","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct physical interaction plus conditional KO with specific cytokine readout, in vivo validation","pmids":["24777530"],"is_preprint":false},{"year":2014,"finding":"Structure-based mutations in Rad50 that promote or destabilize the ATP-bound 'closed' state show that the closed conformation promotes DNA end binding and end tethering, while hydrolysis-induced opening is essential for DNA resection; reducing ATP-bound state stability impairs DNA repair and Tel1/ATM checkpoint signaling in S. pombe, DSB resection in S. cerevisiae, and ATM activation by human MRN in vitro.","method":"Crystal structures, X-ray scattering, biochemical assays, genetic functional analyses in multiple organisms","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures plus multiple biochemical assays plus genetic validation across multiple model organisms","pmids":["24493214"],"is_preprint":false},{"year":2014,"finding":"RAD50 phosphorylation at S635 by ATR is required for ATR signaling through Chk1 and downstream substrates in response to replication stress; RAD50 S635 phosphorylation is essential for DNA replication restart by promoting cohesin loading at stalled replication forks; RAD50 is required for ATR activation in mammalian cells.","method":"Phosphorylation site mutagenesis, functional complementation, replication restart assay, co-immunoprecipitation","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — site-specific mutagenesis with functional readouts, single lab","pmids":["24694934"],"is_preprint":false},{"year":2015,"finding":"Crystal structure of Methanococcus jannaschii MR-ATPγS-DNA shows that partly deformed DNA runs symmetrically across the central groove between two ATPγS-bound Rad50 nucleotide-binding domains; duplex DNA cannot access the Mre11 active site in the ATP-free full-length MR complex; ATP hydrolysis drives rotation of the nucleotide-binding domain inducing DNA melting so substrate DNA can access Mre11.","method":"X-ray crystallography, in vitro biochemical assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus biochemical validation showing ATP-dependent DNA access to nuclease site","pmids":["26717941"],"is_preprint":false},{"year":2015,"finding":"Rad50 hook mutations flanking Zn2+-coordinating cysteines impair hook-mediated dimerization; Mre11 complex functions specified by the globular domain including Tel1/ATM activation, NHEJ, and DSB end resection are affected; these phenotypes are suppressed by mutations within the coiled-coil and globular ATPase domains, indicating conformational changes are transmitted from the hook through the coiled coils to the globular domain.","method":"Yeast genetics, biochemical assays, suppressor analysis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with suppressor analysis and biochemical validation, multiple functional readouts","pmids":["25601756"],"is_preprint":false},{"year":2016,"finding":"Human MRN complex (hMRN) catalyzes sequential endonucleolytic and exonucleolytic activities on both 5' and 3' strands of DNA ends containing protein adducts; NBS1, ATP, and adducts are essential for this function; NBS1 inhibits MRE11/RAD50-catalyzed 3'→5' exonucleolytic degradation of clean DNA ends; phosphorylated CtIP further stimulates hMRN endonucleolytic cleavage.","method":"In vitro nuclease assays with recombinant proteins, mutational analysis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — biochemical reconstitution with defined substrates and multiple mutants, single lab with rigorous controls","pmids":["27814491"],"is_preprint":false},{"year":2016,"finding":"Crystal structure of ATP-bound eukaryotic Rad50 NBD dimer (Chaetomium thermophilum) in complex with DNA shows that a Rad50 dimer binds approximately 18 bp of DNA along the dimer interface in an ATP-dependent fashion, or bridges two DNA ends with a preference for 3' overhangs; a strand-loop-helix motif on Rad50 NBD mediates DNA binding.","method":"X-ray crystallography, SAXS, cross-linking studies, in vitro DNA binding, yeast mutational analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus multiple orthogonal structural methods plus genetic validation in vivo","pmids":["26896444"],"is_preprint":false},{"year":2017,"finding":"RAD50 binds homoduplex DNA and promotes one-dimensional facilitated diffusion of MRN along DNA including nucleosome-coated DNA; MRE11 is required for DNA end recognition and nuclease activities; MRN removes Ku or other DNA adducts via an MRE11-dependent nucleolytic reaction; MRN then loads EXO1 onto free DNA ends and acts as a processivity factor for EXO1 in the presence of RPA.","method":"High-throughput single-molecule microscopy, in vitro reconstitution with purified proteins","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — single-molecule microscopy with reconstituted system, domain-specific mutants, multiple functional readouts","pmids":["28867292"],"is_preprint":false},{"year":2017,"finding":"Human Rad50 hook and coiled-coil domain structure reveals a predominant intracomplex rod-shaped dimer in which the two parallel coiled coils form a rod; a novel interface within the coiled-coil domains stabilizes the Rad50 protomer interaction; in yeast, removal of this coiled-coil interface compromises Tel1/ATM activation without affecting DNA repair.","method":"X-ray crystallography, yeast genetic analysis","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus genetic separation-of-function analysis","pmids":["28134932"],"is_preprint":false},{"year":2017,"finding":"Both ATPase active sites of the Rad50 dimer must be functional for stimulation of ATP hydrolysis by DNA ends, for endonucleolytic cleavage at protein adducts, and for stimulation of ATM kinase activity; double-stranded DNA stimulates ATP hydrolysis by hMRN ~20-fold in an end-dependent manner.","method":"In vitro ATPase assays with catalytic site mutants creating single-active-site Rad50 dimers, in vitro nuclease and ATM kinase assays","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — biochemical reconstitution with specific catalytic mutants, multiple functional readouts, single lab","pmids":["28369545"],"is_preprint":false},{"year":2018,"finding":"The Ku complex shields DNA ends from MRX exonuclease activity but facilitates MRX endonucleolytic scission of the 5'-terminated strand in an ATP- and Sae2-dependent manner; the endonucleolytic incision site is enlarged into a gap via MRX exonuclease activity stimulated by Sae2 without ATP; RPA renders partially resected DNA susceptible to MRX-Sae2; internal protein blocks trigger DNA cleavage by MRX.","method":"In vitro resection assays with purified proteins, yeast genetics","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — independent biochemical reconstitutions from two labs (Cejka and Sung groups) using purified components","pmids":["29321179","29321177"],"is_preprint":false},{"year":2019,"finding":"Cryo-EM structures of bacterial Mre11-Rad50 homolog SbcCD in resting and DNA-bound states reveal: in resting state Mre11 nuclease is blocked by ATP-Rad50; upon DNA binding, the two coiled coils zip up into a rod forming a clamp around dsDNA; Mre11 moves to the side of Rad50, binds the DNA end, and assembles a DNA cutting channel for nuclease reactions.","method":"Cryo-electron microscopy, biochemical validation","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — cryo-EM structures in multiple functional states with biochemical validation","pmids":["31492634"],"is_preprint":false},{"year":2019,"finding":"The ATP-bound 'closed' conformation of the Mre11-Rad50 complex is essential for Tel1/ATM activation; separation-of-function mutants mre11-S499P and rad50-A78T specifically reduce Tel1-MRX interaction and Tel1 association at DSBs; Rad50-A78T destabilizes the ATP-bound conformational state; molecular dynamics simulations confirm that ATP-bound MR complex lingers in a tightly closed conformation.","method":"Yeast genetics, biochemical Tel1 kinase assays, molecular dynamics simulations, ChIP","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic separation-of-function plus biochemical validation plus computational modeling","pmids":["30698745"],"is_preprint":false},{"year":2019,"finding":"Stepwise resection by MRX-Sae2 proceeds through endonucleolytic DNA incisions followed by exonucleolytic 3'→5' degradation of individual DNA fragments; Rad50 restricts Mre11 exonuclease in an ATP binding-dependent manner preventing 3' end degradation; phosphorylated Sae2 overcomes this inhibition to promote MRX 3'→5' exonuclease activity, which requires ATP hydrolysis by Rad50.","method":"In vitro resection assays with purified recombinant proteins and plasmid-length substrates","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 1 / Moderate — biochemical reconstitution with defined substrates and ATP-state mutants, multiple mechanistic readouts","pmids":["30819891"],"is_preprint":false},{"year":2019,"finding":"C1QBP forms a complex (MRC) with MRE11 and RAD50, stabilizing MRE11/RAD50 while inhibiting MRE11 nuclease activity by preventing DNA/chromatin binding; upon DNA damage, ATM phosphorylates MRE11-S676/S678 to dissociate the MRC complex, allowing MRN recruitment to DSBs.","method":"Co-immunoprecipitation, in vitro nuclease assays, mutagenesis, chromatin fractionation","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods identifying new regulatory complex with mechanistic dissection of phosphorylation-dependent dissociation","pmids":["31353207"],"is_preprint":false},{"year":2019,"finding":"Tel1/ATM activation by MRX requires Rad50 ATPase activity and long nucleosome-free dsDNA but not DNA ends; either Mre11 or Xrs2 (but not necessarily both) is required in addition to DNA and Rad50; all three MRX subunits physically associate with Tel1.","method":"In vitro Tel1 kinase assays with purified components, co-immunoprecipitation, systematic mutant analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted in vitro kinase activation with systematic subunit and mutant analysis","pmids":["31073030"],"is_preprint":false},{"year":2022,"finding":"Cryo-EM structure of Chaetomium thermophilum MRN (2:2:1 complex) reveals: single NBS1 wrapping around the autoinhibited Mre11 nuclease dimer; two DNA-binding modes (ATP-dependent for DNA ends, ATP-independent through Mre11 C-terminus); two 60-nm coiled-coil domains forming a linear rod with zinc-hook apices; two MRN complexes can dimerize via hook apices to form 120-nm spanning MRN-MRN structures.","method":"Cryo-electron microscopy, biochemical validation","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — cryo-EM structure of near-complete eukaryotic MRN complex with functional validation","pmids":["36577401"],"is_preprint":false},{"year":2022,"finding":"Cryo-EM structures of bacterial SbcCD (Mre11-Rad50 homolog) bound to protein-blocked DNA end and DNA hairpin show: Mre11-Rad50 bends internal DNA for endonucleolytic cleavage; Mre11 is loaded onto blocked DNA ends with Mre11 pointing away from the block, explaining how 3'→5' exonuclease and endonuclease activities are mechanistically distinguished by the orientation of Mre11-Rad50 on diverse DNA ends.","method":"Cryo-electron microscopy, biochemical nuclease assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — cryo-EM structures in multiple substrate-bound states with biochemical validation","pmids":["35987200"],"is_preprint":false},{"year":2022,"finding":"S. cerevisiae Mre11-Rad50 (with or without Xrs2) forms higher-order oligomeric assemblies in solution and on DNA; Rad50 mediates oligomerization through a conserved beta-sheet; mutations disrupting oligomerization impair foci formation, DNA damage signaling, DSB repair, and telomere maintenance in vivo; oligomerization does not affect exonuclease activity but drives endonucleolytic cleavage at multiple sites on the 5'-DNA strand.","method":"Electron microscopy, biochemical assays, yeast genetic analysis, in vitro nuclease assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods with in vitro and in vivo validation, separation-of-function analysis","pmids":["35501303"],"is_preprint":false}],"current_model":"RAD50 is the ABC-ATPase scaffold subunit of the conserved MRE11-RAD50-NBS1 (MRN) trimeric complex that functions as the primary sensor and processor of DNA double-strand breaks: RAD50 ATP binding drives a 'closed' conformation that promotes DNA end binding, tethering of broken ends (via long coiled-coil arms joined by a zinc-hook homodimerization interface), and ATM/Tel1 kinase activation, while ATP hydrolysis opens the complex to unmask MRE11's nuclease active site, enabling endonucleolytic incision past protein adducts and Ku blocks followed by 5'-strand resection, with NBS1 further modulating these activities by recruiting CtIP and other factors; RAD50 is also phosphorylated by ATM (at Ser-635) and ATR to serve as an adaptor for downstream checkpoint signaling, and can interact with CARD9 in the cytoplasm to link cytosolic DNA sensing to IL-1β production."},"narrative":{"mechanistic_narrative":"RAD50 is the ABC-ATPase scaffold subunit of the conserved MRE11-RAD50-NBS1 (MRN) complex, the primary cellular sensor and processor of DNA double-strand breaks (DSBs) [PMID:8756642, PMID:9590181, PMID:10346816]. RAD50 stably associates with MRE11 to form a (MRE11)2(RAD50)2 heterotetrameric DNA-processing head linked to long coiled-coil arms, with NBS1 completing the trimeric complex required for ionizing-radiation-induced nuclear foci and DSB-checkpoint coupling [PMID:9590181, PMID:11371344]. RAD50 supplies the complex's ATP-binding and hydrolysis activity, which acts as a conformational switch: ATP binding drives a 'closed' state that promotes DNA-end binding, end tethering, and ATM/Tel1 kinase activation, while ATP hydrolysis opens the complex to unmask the MRE11 active site and convert it from endonuclease to exonuclease, enabling endonucleolytic incision past protein adducts and Ku blocks followed by 5'-strand resection [PMID:10346816, PMID:21511873, PMID:22102415, PMID:24493214, PMID:26717941]. The coiled-coil arms terminate in a Zn2+-coordinated zinc-hook dimerization interface that bridges and tethers broken DNA ends across long distances, and conformational changes are transmitted from the hook through the coiled coils to the globular ATPase/nuclease domain [PMID:12152085, PMID:16163361, PMID:25601756]. Both RAD50 ATPase active sites are required for DNA-stimulated ATP hydrolysis, adduct cleavage, and ATM activation, and the complex stimulates ATM by tethering DNA and recruiting downstream factors including CtIP and EXO1 to drive resection [PMID:28867292, PMID:28369545, PMID:15064416, PMID:16622404]. MRN directly activates ATM toward p53, Chk2, and H2AX, and RAD50 is itself phosphorylated by ATM at Ser-635 to act as an adaptor for downstream checkpoint signaling through SMC1 [PMID:15064416, PMID:21757780]. Beyond DSB repair, RAD50 participates in telomere length control via MRN/ATM regulation of TRF1 [PMID:17694070] and, in the cytoplasm, interacts with CARD9 to couple cytosolic dsDNA sensing to NF-κB activation and pro-IL-1β production [PMID:24777530].","teleology":[{"year":1996,"claim":"Established that human RAD50 is the homolog of yeast Rad50 and acts within a multiprotein complex rather than alone, defining the molecular context for all subsequent mechanism.","evidence":"Co-immunoprecipitation and cDNA characterization identifying stable RAD50-MRE11 association","pmids":["8756642"],"confidence":"High","gaps":["Did not define the third subunit","No enzymatic or structural mechanism"]},{"year":1998,"claim":"Identified NBS1 as the third MRN subunit and connected the complex to a human genome-instability disease, linking DSB repair to checkpoint signaling.","evidence":"Gene mapping and immunofluorescence in NBS patient cells showing NBS1 dependence of RAD50/MRE11 IR foci","pmids":["9590181","9315668"],"confidence":"High","gaps":["Mechanism of foci assembly not resolved","Catalytic roles of each subunit unknown"]},{"year":1999,"claim":"Assigned enzymatic functions within the reconstituted complex, showing RAD50 provides ATP binding that switches MRE11 nuclease specificity.","evidence":"Biochemical reconstitution with recombinant NBS1/MRE11/RAD50, nuclease and helicase assays with mutants","pmids":["10346816","11454871"],"confidence":"High","gaps":["Structural basis of the ATP switch not yet visualized","In vivo relevance of ATP-controlled specificity not tested"]},{"year":2002,"claim":"Resolved the structural architecture: RAD50 is an ABC-ATPase whose coiled coils end in a Zn2+ zinc-hook dimer interface enabling long-range DNA tethering.","evidence":"X-ray crystallography of archaeal Rad50/Mre11, EM, and yeast genetics of zinc-hook mutants","pmids":["11371344","12152085","14698290"],"confidence":"High","gaps":["How hook signal propagates to the catalytic head not yet shown","Eukaryotic full-complex architecture unresolved"]},{"year":2004,"claim":"Demonstrated that MRN directly activates ATM kinase, establishing RAD50's complex as an upstream signaling activator and not merely a repair enzyme.","evidence":"In vitro kinase assays with recombinant MRN and ATM substrates p53, Chk2, H2AX","pmids":["15064416"],"confidence":"High","gaps":["Did not separate tethering from direct activation contributions","RAD50-specific contribution to ATM activation not isolated"]},{"year":2005,"claim":"Visualized the DNA-induced conformational change that converts intracomplex coiled-coil interactions to intercomplex tethering, providing a physical mechanism for end bridging.","evidence":"Atomic force and electron microscopy and single-molecule imaging of hRAD50/MRE11/NBS1 on DNA","pmids":["16163361"],"confidence":"High","gaps":["Coupling to ATP cycle quantitative detail incomplete","Nuclease activation step not captured"]},{"year":2006,"claim":"Clarified that MRN promotes ATM activation in two steps, with RAD50-mediated DNA tethering increasing local ATM concentration to drive monomer conversion.","evidence":"Reconstitution in Xenopus cell-free extracts with NBS1 ATM-binding-domain mutants","pmids":["16622404"],"confidence":"High","gaps":["RAD50 ATPase-state requirement not directly tested here","In-cell ordering of steps not established"]},{"year":2011,"claim":"Defined the ATP-driven molecular switch at atomic resolution and tied RAD50 Ser-635 ATM phosphorylation to downstream checkpoint signaling.","evidence":"Mre11-Rad50-ATPγS crystal structure with biochemistry; phosphosite mapping and S635G complementation in RAD50-deficient cells","pmids":["21511873","22102415","21757780"],"confidence":"High","gaps":["Kinetics of the endo-to-exo transition in vivo not measured","S635 effector pathway beyond SMC1 incompletely mapped"]},{"year":2013,"claim":"Showed RAD50 ATPase activity directly powers DNA-end unwinding required for resection, linking the catalytic cycle to repair output in human cells.","evidence":"Single-molecule FRET unwinding assays with RAD50 catalytic mutants plus cellular repair assays","pmids":["24191051"],"confidence":"High","gaps":["Coupling of unwinding to nucleolytic incision not fully resolved","Role of accessory factors during unwinding not addressed"]},{"year":2014,"claim":"Established the structural separation between the closed-state tethering/signaling function and hydrolysis-driven opening required for resection, and revealed a cytoplasmic RAD50-CARD9 innate-immune role.","evidence":"Structure-based Rad50 mutants across organisms; RAD50-CARD9 Co-IP and conditional-knockout cytokine and infection assays","pmids":["24493214","24777530","24694934"],"confidence":"High","gaps":["Structural basis of RAD50-CARD9 interaction unknown","Crosstalk between nuclear repair and cytoplasmic immune roles unexplored"]},{"year":2017,"claim":"Demonstrated that both RAD50 ATPase sites are jointly required for adduct cleavage and ATM activation, and that RAD50 enables MRN to translocate on DNA and load EXO1 for processive resection.","evidence":"Single-active-site Rad50 dimer mutants in ATPase/nuclease/ATM assays; single-molecule microscopy of MRN-EXO1 on DNA","pmids":["28369545","28867292","28134932"],"confidence":"High","gaps":["Coordination of the two active sites in vivo not directly observed","Adduct-specificity determinants incompletely defined"]},{"year":2019,"claim":"Resolved the conformational mechanics of DNA clamping and nuclease loading and identified C1QBP as a phosphorylation-controlled negative regulator of MRE11/RAD50 nuclease.","evidence":"Cryo-EM of SbcCD resting and DNA-bound states; Co-IP, nuclease, and ATM-phosphosite analysis of the C1QBP-MRE11-RAD50 complex","pmids":["31492634","31353207","30819891"],"confidence":"High","gaps":["Eukaryotic full-complex conformational cycle not yet at high resolution","Regulation of C1QBP dissociation timing in cells incomplete"]},{"year":2022,"claim":"Delivered near-complete eukaryotic MRN architecture and RAD50-mediated higher-order oligomerization, explaining how RAD50 orients MRE11 for distinct endo- versus exonucleolytic cuts and bridges paired complexes.","evidence":"Cryo-EM of C. thermophilum MRN and SbcCD on diverse substrates; EM and yeast genetics of Rad50 oligomerization mutants","pmids":["36577401","35987200","35501303"],"confidence":"High","gaps":["Functional role of MRN-MRN dimerization in cells incompletely defined","Mechanism converting orientation to substrate selection not fully resolved"]},{"year":null,"claim":"How RAD50's nuclear DSB-processing functions are coordinated with its cytoplasmic innate-immune signaling role, and the structural basis of RAD50-CARD9 dsDNA sensing, remain open.","evidence":"No reconstitution or structural study in the timeline connecting the two compartmental roles","pmids":[],"confidence":"Medium","gaps":["No structure of the dsDNA-RAD50-CARD9 complex","No mechanism partitioning RAD50 between nucleus and cytoplasm","Disease-causing RAD50 mutation effects on either role not characterized in this corpus"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[4,11,22,24,27,35]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[15,32,33]},{"term_id":"GO:0140097","term_label":"catalytic activity, acting on DNA","supporting_discovery_ids":[4,7,31,33,39]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[4,7,22,24,31]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[6,9,15,42]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[18]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,2,8]},{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[1,14]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[26]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[5,17]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[0,2,4,31,33]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[12,16,23,27]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[13,28]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[26]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[5,17]}],"complexes":["MRN complex (MRE11-RAD50-NBS1)","MRX complex (Mre11-Rad50-Xrs2)","MRC complex (MRE11-RAD50-C1QBP)"],"partners":["MRE11","NBS1","BRCA1","CTIP","EXO1","C1QBP","CARD9","RINT-1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q92878","full_name":"DNA repair protein RAD50","aliases":[],"length_aa":1312,"mass_kda":153.9,"function":"Component of the MRN complex, which plays a central role in double-strand break (DSB) repair, DNA recombination, maintenance of telomere integrity and meiosis (PubMed:15064416, PubMed:21757780, PubMed:27889449, PubMed:28134932, PubMed:28867292, PubMed:9590181, PubMed:9651580, PubMed:9705271). The MRN complex is involved in the repair of DNA double-strand breaks (DSBs) via homologous recombination (HR), an error-free mechanism which primarily occurs during S and G2 phases (PubMed:15064416, PubMed:21757780, PubMed:27889449, PubMed:28867292, PubMed:9590181, PubMed:9651580, PubMed:9705271). The complex (1) mediates the end resection of damaged DNA, which generates proper single-stranded DNA, a key initial steps in HR, and is (2) required for the recruitment of other repair factors and efficient activation of ATM and ATR upon DNA damage (PubMed:15064416, PubMed:27889449, PubMed:28867292, PubMed:9590181, PubMed:9651580, PubMed:9705271). The MRN complex possesses single-strand endonuclease activity and double-strand-specific 3'-5' exonuclease activity, which are provided by MRE11, to initiate end resection, which is required for single-strand invasion and recombination (PubMed:11741547, PubMed:9590181, PubMed:9651580, PubMed:9705271). Within the complex, RAD50 is both required to bind DNA ends and hold them in close proximity and regulate the activity of MRE11 (PubMed:11741547, PubMed:12805565, PubMed:28134932). RAD50 provides an ATP-dependent control of MRE11 by positioning DNA ends into the MRE11 active site: ATP-binding induces a large structural change from an open form with accessible MRE11 nuclease sites into a closed form (By similarity). The MRN complex is also required for DNA damage signaling via activation of the ATM and ATR kinases: the nuclease activity of MRE11 is not required to activate ATM and ATR (PubMed:15064416, PubMed:15790808, PubMed:16622404). The MRN complex is also required for the processing of R-loops (PubMed:31537797). In telomeres the MRN complex may modulate t-loop formation (PubMed:10888888)","subcellular_location":"Nucleus; Chromosome, telomere; Chromosome","url":"https://www.uniprot.org/uniprotkb/Q92878/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RAD50","classification":"Not Classified","n_dependent_lines":86,"n_total_lines":1208,"dependency_fraction":0.07119205298013245},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"BOP1","stoichiometry":4.0},{"gene":"CSK","stoichiometry":0.2},{"gene":"EPN2","stoichiometry":0.2},{"gene":"FNBP1","stoichiometry":0.2},{"gene":"HIST2H2BE","stoichiometry":0.2},{"gene":"HMGN5","stoichiometry":0.2},{"gene":"MYO1E","stoichiometry":0.2},{"gene":"NCK1","stoichiometry":0.2},{"gene":"NECAP1","stoichiometry":0.2},{"gene":"NUMA1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/RAD50","total_profiled":1310},"omim":[{"mim_id":"621363","title":"MAP7 DOMAIN-CONTAINING PROTEIN 1; MAP7D1","url":"https://www.omim.org/entry/621363"},{"mim_id":"618641","title":"INFANTILE LIVER FAILURE SYNDROME 3; ILFS3","url":"https://www.omim.org/entry/618641"},{"mim_id":"617154","title":"MRN COMPLEX-INTERACTING PROTEIN; MRNIP","url":"https://www.omim.org/entry/617154"},{"mim_id":"616940","title":"EXONUCLEASE 3-PRIME-TO-5-PRIME DOMAIN-CONTAINING PROTEIN 2; EXD2","url":"https://www.omim.org/entry/616940"},{"mim_id":"613984","title":"FANCD2 GENE; FANCD2","url":"https://www.omim.org/entry/613984"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Nuclear bodies","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RAD50"},"hgnc":{"alias_symbol":["hRad50","RAD50-2"],"prev_symbol":[]},"alphafold":{"accession":"Q92878","domains":[{"cath_id":"3.40.50.300","chopping":"2-147_1228-1261_1268-1312","consensus_level":"medium","plddt":86.5499,"start":2,"end":1312},{"cath_id":"1.10.287","chopping":"609-778","consensus_level":"high","plddt":85.1173,"start":609,"end":778}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q92878","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q92878-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q92878-F1-predicted_aligned_error_v6.png","plddt_mean":82.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RAD50","jax_strain_url":"https://www.jax.org/strain/search?query=RAD50"},"sequence":{"accession":"Q92878","fasta_url":"https://rest.uniprot.org/uniprotkb/Q92878.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q92878/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q92878"}},"corpus_meta":[{"pmid":"9590181","id":"PMC_9590181","title":"The 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p95 deficiency abrogates formation of hMRE11/hRAD50 ionizing radiation-induced foci, linking DSB repair to cell cycle checkpoint functions.\",\n      \"method\": \"Gene mapping, immunofluorescence, cell biology in NBS patient-derived cells\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods, replicated across labs, foundational complex identification\",\n      \"pmids\": [\"9590181\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"BRCA1 interacts in vitro and in vivo with hRAD50 (which forms a complex with hMRE11 and p95/nibrin); upon irradiation, BRCA1 co-localizes with hRAD50 in nuclear foci, and wild-type BRCA1 is required for formation of these foci and for cellular resistance to DNA damage.\",\n      \"method\": \"In vitro binding assay, co-immunoprecipitation, immunofluorescence colocalization\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP plus in vitro binding plus functional rescue experiment\",\n      \"pmids\": [\"10426999\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The triple complex of recombinant NBS1, MRE11, and RAD50 displays ATP-stimulated DNA unwinding and efficient cleavage of fully paired hairpins not seen with MRE11/RAD50 alone; RAD50 is responsible for ATP binding by the complex, and ATP controls a switch in endonuclease specificity allowing cleavage of 3'-protruding strands at double-/single-strand transitions.\",\n      \"method\": \"Biochemical reconstitution with recombinant proteins, mutational analysis, in vitro nuclease/helicase assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution with purified recombinant proteins and mutagenesis, replicated by multiple labs\",\n      \"pmids\": [\"10346816\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"A small fraction of RAD50, MRE11, and NBS1 is associated with TRF2 immunocomplexes; RAD50 and MRE11 localize to interphase telomeres, and NBS1 associates with TRF2 and telomeres specifically in S phase but not G1 or G2, indicating cell-cycle-regulated association of MRN with telomeres.\",\n      \"method\": \"Nanoelectrospray tandem mass spectrometry, protein blotting, indirect immunofluorescence\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mass spectrometry identification plus immunofluorescence localization, replicated across multiple subsequent studies\",\n      \"pmids\": [\"10888888\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Crystal structures of Pyrococcus furiosus Mre11 reveal a protein phosphatase-like dimanganese-binding nuclease domain; the structure of P. furiosus Rad50 ABC-ATPase with adjacent coiled-coil defines a compact Mre11/Rad50-ATPase complex and suggests that Rad50 ATP-driven conformational switching directly controls the Mre11 exonuclease; the MR complex exists as a (Mre11)2/(Rad50)2 heterotetrameric DNA-processing head with a double coiled-coil linker.\",\n      \"method\": \"X-ray crystallography, electron microscopy, small-angle X-ray scattering, ultracentrifugation\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures with multiple orthogonal structural methods and functional mapping\",\n      \"pmids\": [\"11371344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Purified yeast Rad50 and Mre11 form a stable equimolar complex. Mre11 has 3'→5' exonuclease activity releasing mononucleotides; addition of Rad50 does not significantly alter this exonuclease activity. Mre11 has endonuclease activity on hairpins and 3' ssDNA tails, and these endonuclease activities are markedly enhanced by Rad50 only in the presence of ATP.\",\n      \"method\": \"Protein purification, in vitro nuclease assays, ATP-dependence studies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro biochemical reconstitution with purified proteins, multiple substrates tested\",\n      \"pmids\": [\"11454871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"NBS1 C-terminal sequence (residues 665-693) is essential for hMRE11 binding and is necessary for nuclear localization of the MRE11/RAD50 complex and cellular radiation resistance; the N-terminal FHA domain regulates nuclear foci formation in response to DNA damage but is not essential for nuclear transport or radiation resistance.\",\n      \"method\": \"Deletion mutagenesis, co-immunoprecipitation, cellular localization experiments, radiation sensitivity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — structure-function mutagenesis with cellular validation, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"11062235\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The Rad50 coiled-coil region contains a zinc-hook dimer interface where pairs of conserved Cys-X-X-Cys motifs form interlocking hooks that bind one Zn2+ ion; these hooks join oppositely protruding Rad50 coiled-coil domains to form a flexible bridge of up to 1,200 Å, enabling DNA tethering. Mutations in this zinc-hook motif confer radiation sensitivity in yeast and disrupt binding at the distant Mre11 nuclease interface.\",\n      \"method\": \"X-ray crystallography (2.2 Å), electron microscopy, biochemical assays, yeast genetics\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus EM plus biochemical and genetic validation, multiple orthogonal methods\",\n      \"pmids\": [\"12152085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Rad50 ATP-binding domains share structural and mechanistic conservation with ABC transporters; ATP binding drives conformational changes in substrate-specific domains, functioning as a chemo-mechanical device in DNA repair.\",\n      \"method\": \"Structural analysis, comparative crystallography\",\n      \"journal\": \"Current opinion in structural biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — structural analysis reviewed, but primarily a synthesis/review perspective without new experimental validation\",\n      \"pmids\": [\"12727520\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Rad50 S793R signature motif mutation prevents ATP binding and disrupts communication among other ATP-binding loops, prevents Rad50 dimerization; the equivalent mutation in human RAD50 forms a complex with MRE11 and NBS1 but is specifically deficient in all ATP-dependent enzymatic activities; the same mutation in S. cerevisiae fails to complement rad50 deletion in DNA repair assays.\",\n      \"method\": \"X-ray crystallography, biochemical ATPase assays, yeast genetic complementation\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus mutagenesis plus in vitro biochemistry plus in vivo genetic validation\",\n      \"pmids\": [\"14698290\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The MRN complex directly activates ATM kinase activity in vitro toward substrates p53, Chk2, and histone H2AX; MRN makes multiple contacts with ATM and stimulates ATM activity by facilitating stable substrate binding; phosphorylation of NBS1 is critical for MRN stimulation of ATM activity toward Chk2 but not p53.\",\n      \"method\": \"In vitro kinase assays with recombinant proteins, protein interaction studies\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified recombinant components, multiple substrates and mutants tested\",\n      \"pmids\": [\"15064416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"A novel RAD50-interacting protein, RINT-1, was identified via yeast two-hybrid screening; RINT-1 binds specifically to RAD50 during late S and G2/M phases of the cell cycle; cells expressing truncated RINT-1 display a defective radiation-induced G2/M checkpoint.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, cell cycle analysis, checkpoint assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — yeast two-hybrid plus co-IP with functional phenotype, single lab\",\n      \"pmids\": [\"11096100\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"RPA and the MRN complex (MRE11, RAD50, NBS1) co-localize to discrete nuclear foci and physically interact in response to DNA replication fork blockage by HU or UV; co-immunoprecipitation of RPA with anti-RAD50 antibody was demonstrated; phosphorylation of both RPA and MRE11 is required for this interaction.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence, subcellular fractionation, phosphatase treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP with multiple antibodies plus fractionation, single lab\",\n      \"pmids\": [\"15180989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"DNA binding by the hRAD50/MRE11/NBS1 globular domain leads to parallel orientation of the coiled coils, preventing intracomplex interactions and favoring intercomplex associations needed for DNA tethering; this conformational change is transmitted 50 nm from the DNA-binding domain to the coiled-coil apices.\",\n      \"method\": \"Atomic force microscopy, electron microscopy, single-molecule imaging\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct structural/biophysical visualization of conformational change upon DNA binding, single lab with rigorous single-molecule methods\",\n      \"pmids\": [\"16163361\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ATM activation by DSBs occurs in two steps: first, dimeric ATM is recruited to damaged DNA and dissociates into monomers (facilitated by MRN tethering DNA to increase local concentration); second, the ATM-binding domain of NBS1 is required and sufficient to convert unphosphorylated ATM monomers into enzymatically active monomers in the absence of DNA.\",\n      \"method\": \"Biochemical reconstitution, Xenopus cell-free extract system, mutational analysis\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution in cell-free system with defined mutants, multiple orthogonal approaches\",\n      \"pmids\": [\"16622404\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"MRE11-RAD50-NBS1 and ATM function as co-mediators of TRF1 in telomere length control; RAD50 targeted to telomeres downregulates TRF1 association with telomeric DNA; ATM-mediated phosphorylation of TRF1 impairs its ability to bind telomeric DNA in vitro, and MRN is required for this TRF1 phosphorylation by ATM.\",\n      \"method\": \"Chromatin immunoprecipitation, telomere-targeted overexpression, in vitro DNA binding assays, RNAi knockdown\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple methods including in vitro binding and cellular experiments, single lab\",\n      \"pmids\": [\"17694070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Mre11/Rad50 complexes from three organisms (human, yeast, archaeal) catalyze the reversible adenylate kinase reaction in vitro; mutation of the conserved signature motif reduces adenylate kinase activity without reducing ATP hydrolysis; this mutant resembles a rad50 null strain for meiosis and telomere maintenance; adenylate kinase inhibitor blocks Mre11/Rad50-dependent DNA tethering in vitro and in cell-free extracts.\",\n      \"method\": \"In vitro enzymatic assays, yeast genetics, pharmacological inhibition, cell-free extract DNA tethering assay\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with multiple organisms, mutagenesis, genetic and chemical validation\",\n      \"pmids\": [\"17349953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"NBS1 FHA domain recruits phosphorylated Ctp1 to DSBs via binding of the NBS1 FHA domain to a Ctp1 pThr-Asp motif; fission yeast and human NBS1 structures reveal fused FHA-BRCT1-BRCT2 domains flexibly linked to C-terminal Mre11- and ATM-binding motifs; Nbs1 tethers Ctp1/CtIP to the immediate vicinity of DSBs to restrict DNA end processing activities.\",\n      \"method\": \"X-ray crystallography, SAXS, genetic analysis, biochemical binding assays\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures plus SAXS plus genetic and biochemical validation, multiple orthogonal methods\",\n      \"pmids\": [\"19804755\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Biochemical reconstitution of DNA end resection shows that the yeast MRX complex and Sae2 stimulate Exo1-mediated 5' strand degradation through cooperative binding of DNA substrates; MRX recruits Dna2 nuclease to DSB ends and stimulates recruitment of Exo1 while antagonizing excess Ku binding to DSB ends.\",\n      \"method\": \"In vitro resection reconstitution with purified proteins, ChIP in yeast\",\n      \"journal\": \"Nature; The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — independent biochemical reconstitutions in two labs (Kowalczykowski and Lee/Ira groups)\",\n      \"pmids\": [\"20811461\", \"20834227\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"MRX and Sae2 directly promote 5' strand resection; reconstitution with purified MRX, Sae2, and Exo1 shows that 5' strand degradation is catalyzed by Exo1 yet completely dependent on MRX and Sae2 when Exo1 levels are limiting, mainly through cooperative DNA substrate binding.\",\n      \"method\": \"In vitro resection reconstitution with purified recombinant proteins\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — biochemical reconstitution with purified components, replicated across labs\",\n      \"pmids\": [\"21102445\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Crystal structure of the Mre11-Rad50-ATPγS complex shows Mre11 promotes ATPase activity of Rad50 by holding the coiled-coil arm and stabilizing the signature motif and P-loop; ATP-bound Rad50 negatively regulates Mre11 nuclease activity by blocking the Mre11 active site; ATP hydrolysis disengages Rad50 molecules and causes conformational change in Mre11's flexible linker to unmask the Mre11 active site.\",\n      \"method\": \"X-ray crystallography, biochemical ATPase and nuclease assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus biochemical validation, multiple orthogonal methods\",\n      \"pmids\": [\"21511873\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"ATM phosphorylates RAD50 at Ser-635; a RAD50 S635G phosphosite mutant supports normal ATM activation but is defective in correcting DNA damage-induced signaling through ATM-dependent substrate SMC1, fails to correct radiosensitivity, DSB repair, and S-phase checkpoint defects, without disrupting MRE11/RAD50/NBS1 complex integrity.\",\n      \"method\": \"Phosphorylation site mapping, site-directed mutagenesis, functional complementation in RAD50-deficient cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — specific phosphosite identified and validated by mutagenesis with multiple functional readouts, single lab\",\n      \"pmids\": [\"21757780\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"ATP binding to RAD50 induces a closed conformation in which MRE11 functions as an endonuclease; ATP hydrolysis opens the RAD50-MRE11 complex and MRE11 maintains exonuclease activity. Thus, ATP hydrolysis acts as a molecular switch converting MRE11 from endonuclease to exonuclease.\",\n      \"method\": \"In vitro nuclease assays, EM visualization of conformational states, ATP binding/hydrolysis studies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with conformational visualization plus functional nuclease assays, single lab\",\n      \"pmids\": [\"22102415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"MRN complex visualized by single-molecule FRET unwinds 15-20 base pairs at the end of a duplex DNA molecule, holding the branched structure open for minutes in an ATP-dependent reaction; a Rad50 catalytic domain mutant deficient in this ATP-dependent DNA unwinding is impaired in DNA end resection in vitro and in resection-dependent repair in human cells.\",\n      \"method\": \"Single-molecule FRET, in vitro resection assays, human cell DNA repair assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — single-molecule biophysics plus mutagenesis plus cellular validation, multiple orthogonal methods\",\n      \"pmids\": [\"24191051\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"RAD50 interacts directly with innate immune adaptor CARD9 in the cytoplasm; dsDNA induces formation of dsDNA-RAD50-CARD9 signaling complexes activating NF-κB and generating pro-IL-1β; cells conditionally deficient in RAD50 exhibit defective DNA-induced IL-1β production.\",\n      \"method\": \"Co-immunoprecipitation, conditional knockout cells, cytokine assays, in vivo infection model\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct physical interaction plus conditional KO with specific cytokine readout, in vivo validation\",\n      \"pmids\": [\"24777530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Structure-based mutations in Rad50 that promote or destabilize the ATP-bound 'closed' state show that the closed conformation promotes DNA end binding and end tethering, while hydrolysis-induced opening is essential for DNA resection; reducing ATP-bound state stability impairs DNA repair and Tel1/ATM checkpoint signaling in S. pombe, DSB resection in S. cerevisiae, and ATM activation by human MRN in vitro.\",\n      \"method\": \"Crystal structures, X-ray scattering, biochemical assays, genetic functional analyses in multiple organisms\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures plus multiple biochemical assays plus genetic validation across multiple model organisms\",\n      \"pmids\": [\"24493214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"RAD50 phosphorylation at S635 by ATR is required for ATR signaling through Chk1 and downstream substrates in response to replication stress; RAD50 S635 phosphorylation is essential for DNA replication restart by promoting cohesin loading at stalled replication forks; RAD50 is required for ATR activation in mammalian cells.\",\n      \"method\": \"Phosphorylation site mutagenesis, functional complementation, replication restart assay, co-immunoprecipitation\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — site-specific mutagenesis with functional readouts, single lab\",\n      \"pmids\": [\"24694934\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Crystal structure of Methanococcus jannaschii MR-ATPγS-DNA shows that partly deformed DNA runs symmetrically across the central groove between two ATPγS-bound Rad50 nucleotide-binding domains; duplex DNA cannot access the Mre11 active site in the ATP-free full-length MR complex; ATP hydrolysis drives rotation of the nucleotide-binding domain inducing DNA melting so substrate DNA can access Mre11.\",\n      \"method\": \"X-ray crystallography, in vitro biochemical assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus biochemical validation showing ATP-dependent DNA access to nuclease site\",\n      \"pmids\": [\"26717941\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Rad50 hook mutations flanking Zn2+-coordinating cysteines impair hook-mediated dimerization; Mre11 complex functions specified by the globular domain including Tel1/ATM activation, NHEJ, and DSB end resection are affected; these phenotypes are suppressed by mutations within the coiled-coil and globular ATPase domains, indicating conformational changes are transmitted from the hook through the coiled coils to the globular domain.\",\n      \"method\": \"Yeast genetics, biochemical assays, suppressor analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with suppressor analysis and biochemical validation, multiple functional readouts\",\n      \"pmids\": [\"25601756\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Human MRN complex (hMRN) catalyzes sequential endonucleolytic and exonucleolytic activities on both 5' and 3' strands of DNA ends containing protein adducts; NBS1, ATP, and adducts are essential for this function; NBS1 inhibits MRE11/RAD50-catalyzed 3'→5' exonucleolytic degradation of clean DNA ends; phosphorylated CtIP further stimulates hMRN endonucleolytic cleavage.\",\n      \"method\": \"In vitro nuclease assays with recombinant proteins, mutational analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — biochemical reconstitution with defined substrates and multiple mutants, single lab with rigorous controls\",\n      \"pmids\": [\"27814491\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Crystal structure of ATP-bound eukaryotic Rad50 NBD dimer (Chaetomium thermophilum) in complex with DNA shows that a Rad50 dimer binds approximately 18 bp of DNA along the dimer interface in an ATP-dependent fashion, or bridges two DNA ends with a preference for 3' overhangs; a strand-loop-helix motif on Rad50 NBD mediates DNA binding.\",\n      \"method\": \"X-ray crystallography, SAXS, cross-linking studies, in vitro DNA binding, yeast mutational analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus multiple orthogonal structural methods plus genetic validation in vivo\",\n      \"pmids\": [\"26896444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"RAD50 binds homoduplex DNA and promotes one-dimensional facilitated diffusion of MRN along DNA including nucleosome-coated DNA; MRE11 is required for DNA end recognition and nuclease activities; MRN removes Ku or other DNA adducts via an MRE11-dependent nucleolytic reaction; MRN then loads EXO1 onto free DNA ends and acts as a processivity factor for EXO1 in the presence of RPA.\",\n      \"method\": \"High-throughput single-molecule microscopy, in vitro reconstitution with purified proteins\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — single-molecule microscopy with reconstituted system, domain-specific mutants, multiple functional readouts\",\n      \"pmids\": [\"28867292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Human Rad50 hook and coiled-coil domain structure reveals a predominant intracomplex rod-shaped dimer in which the two parallel coiled coils form a rod; a novel interface within the coiled-coil domains stabilizes the Rad50 protomer interaction; in yeast, removal of this coiled-coil interface compromises Tel1/ATM activation without affecting DNA repair.\",\n      \"method\": \"X-ray crystallography, yeast genetic analysis\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus genetic separation-of-function analysis\",\n      \"pmids\": [\"28134932\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Both ATPase active sites of the Rad50 dimer must be functional for stimulation of ATP hydrolysis by DNA ends, for endonucleolytic cleavage at protein adducts, and for stimulation of ATM kinase activity; double-stranded DNA stimulates ATP hydrolysis by hMRN ~20-fold in an end-dependent manner.\",\n      \"method\": \"In vitro ATPase assays with catalytic site mutants creating single-active-site Rad50 dimers, in vitro nuclease and ATM kinase assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — biochemical reconstitution with specific catalytic mutants, multiple functional readouts, single lab\",\n      \"pmids\": [\"28369545\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The Ku complex shields DNA ends from MRX exonuclease activity but facilitates MRX endonucleolytic scission of the 5'-terminated strand in an ATP- and Sae2-dependent manner; the endonucleolytic incision site is enlarged into a gap via MRX exonuclease activity stimulated by Sae2 without ATP; RPA renders partially resected DNA susceptible to MRX-Sae2; internal protein blocks trigger DNA cleavage by MRX.\",\n      \"method\": \"In vitro resection assays with purified proteins, yeast genetics\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — independent biochemical reconstitutions from two labs (Cejka and Sung groups) using purified components\",\n      \"pmids\": [\"29321179\", \"29321177\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Cryo-EM structures of bacterial Mre11-Rad50 homolog SbcCD in resting and DNA-bound states reveal: in resting state Mre11 nuclease is blocked by ATP-Rad50; upon DNA binding, the two coiled coils zip up into a rod forming a clamp around dsDNA; Mre11 moves to the side of Rad50, binds the DNA end, and assembles a DNA cutting channel for nuclease reactions.\",\n      \"method\": \"Cryo-electron microscopy, biochemical validation\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — cryo-EM structures in multiple functional states with biochemical validation\",\n      \"pmids\": [\"31492634\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The ATP-bound 'closed' conformation of the Mre11-Rad50 complex is essential for Tel1/ATM activation; separation-of-function mutants mre11-S499P and rad50-A78T specifically reduce Tel1-MRX interaction and Tel1 association at DSBs; Rad50-A78T destabilizes the ATP-bound conformational state; molecular dynamics simulations confirm that ATP-bound MR complex lingers in a tightly closed conformation.\",\n      \"method\": \"Yeast genetics, biochemical Tel1 kinase assays, molecular dynamics simulations, ChIP\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic separation-of-function plus biochemical validation plus computational modeling\",\n      \"pmids\": [\"30698745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Stepwise resection by MRX-Sae2 proceeds through endonucleolytic DNA incisions followed by exonucleolytic 3'→5' degradation of individual DNA fragments; Rad50 restricts Mre11 exonuclease in an ATP binding-dependent manner preventing 3' end degradation; phosphorylated Sae2 overcomes this inhibition to promote MRX 3'→5' exonuclease activity, which requires ATP hydrolysis by Rad50.\",\n      \"method\": \"In vitro resection assays with purified recombinant proteins and plasmid-length substrates\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — biochemical reconstitution with defined substrates and ATP-state mutants, multiple mechanistic readouts\",\n      \"pmids\": [\"30819891\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"C1QBP forms a complex (MRC) with MRE11 and RAD50, stabilizing MRE11/RAD50 while inhibiting MRE11 nuclease activity by preventing DNA/chromatin binding; upon DNA damage, ATM phosphorylates MRE11-S676/S678 to dissociate the MRC complex, allowing MRN recruitment to DSBs.\",\n      \"method\": \"Co-immunoprecipitation, in vitro nuclease assays, mutagenesis, chromatin fractionation\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods identifying new regulatory complex with mechanistic dissection of phosphorylation-dependent dissociation\",\n      \"pmids\": [\"31353207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Tel1/ATM activation by MRX requires Rad50 ATPase activity and long nucleosome-free dsDNA but not DNA ends; either Mre11 or Xrs2 (but not necessarily both) is required in addition to DNA and Rad50; all three MRX subunits physically associate with Tel1.\",\n      \"method\": \"In vitro Tel1 kinase assays with purified components, co-immunoprecipitation, systematic mutant analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted in vitro kinase activation with systematic subunit and mutant analysis\",\n      \"pmids\": [\"31073030\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cryo-EM structure of Chaetomium thermophilum MRN (2:2:1 complex) reveals: single NBS1 wrapping around the autoinhibited Mre11 nuclease dimer; two DNA-binding modes (ATP-dependent for DNA ends, ATP-independent through Mre11 C-terminus); two 60-nm coiled-coil domains forming a linear rod with zinc-hook apices; two MRN complexes can dimerize via hook apices to form 120-nm spanning MRN-MRN structures.\",\n      \"method\": \"Cryo-electron microscopy, biochemical validation\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — cryo-EM structure of near-complete eukaryotic MRN complex with functional validation\",\n      \"pmids\": [\"36577401\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cryo-EM structures of bacterial SbcCD (Mre11-Rad50 homolog) bound to protein-blocked DNA end and DNA hairpin show: Mre11-Rad50 bends internal DNA for endonucleolytic cleavage; Mre11 is loaded onto blocked DNA ends with Mre11 pointing away from the block, explaining how 3'→5' exonuclease and endonuclease activities are mechanistically distinguished by the orientation of Mre11-Rad50 on diverse DNA ends.\",\n      \"method\": \"Cryo-electron microscopy, biochemical nuclease assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — cryo-EM structures in multiple substrate-bound states with biochemical validation\",\n      \"pmids\": [\"35987200\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"S. cerevisiae Mre11-Rad50 (with or without Xrs2) forms higher-order oligomeric assemblies in solution and on DNA; Rad50 mediates oligomerization through a conserved beta-sheet; mutations disrupting oligomerization impair foci formation, DNA damage signaling, DSB repair, and telomere maintenance in vivo; oligomerization does not affect exonuclease activity but drives endonucleolytic cleavage at multiple sites on the 5'-DNA strand.\",\n      \"method\": \"Electron microscopy, biochemical assays, yeast genetic analysis, in vitro nuclease assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods with in vitro and in vivo validation, separation-of-function analysis\",\n      \"pmids\": [\"35501303\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RAD50 is the ABC-ATPase scaffold subunit of the conserved MRE11-RAD50-NBS1 (MRN) trimeric complex that functions as the primary sensor and processor of DNA double-strand breaks: RAD50 ATP binding drives a 'closed' conformation that promotes DNA end binding, tethering of broken ends (via long coiled-coil arms joined by a zinc-hook homodimerization interface), and ATM/Tel1 kinase activation, while ATP hydrolysis opens the complex to unmask MRE11's nuclease active site, enabling endonucleolytic incision past protein adducts and Ku blocks followed by 5'-strand resection, with NBS1 further modulating these activities by recruiting CtIP and other factors; RAD50 is also phosphorylated by ATM (at Ser-635) and ATR to serve as an adaptor for downstream checkpoint signaling, and can interact with CARD9 in the cytoplasm to link cytosolic DNA sensing to IL-1β production.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"RAD50 is the ABC-ATPase scaffold subunit of the conserved MRE11-RAD50-NBS1 (MRN) complex, the primary cellular sensor and processor of DNA double-strand breaks (DSBs) [#0, #2, #4]. RAD50 stably associates with MRE11 to form a (MRE11)2(RAD50)2 heterotetrameric DNA-processing head linked to long coiled-coil arms, with NBS1 completing the trimeric complex required for ionizing-radiation-induced nuclear foci and DSB-checkpoint coupling [#2, #6]. RAD50 supplies the complex's ATP-binding and hydrolysis activity, which acts as a conformational switch: ATP binding drives a 'closed' state that promotes DNA-end binding, end tethering, and ATM/Tel1 kinase activation, while ATP hydrolysis opens the complex to unmask the MRE11 active site and convert it from endonuclease to exonuclease, enabling endonucleolytic incision past protein adducts and Ku blocks followed by 5'-strand resection [#4, #22, #24, #27, #29]. The coiled-coil arms terminate in a Zn2+-coordinated zinc-hook dimerization interface that bridges and tethers broken DNA ends across long distances, and conformational changes are transmitted from the hook through the coiled coils to the globular ATPase/nuclease domain [#9, #15, #30]. Both RAD50 ATPase active sites are required for DNA-stimulated ATP hydrolysis, adduct cleavage, and ATM activation, and the complex stimulates ATM by tethering DNA and recruiting downstream factors including CtIP and EXO1 to drive resection [#33, #35, #12, #16]. MRN directly activates ATM toward p53, Chk2, and H2AX, and RAD50 is itself phosphorylated by ATM at Ser-635 to act as an adaptor for downstream checkpoint signaling through SMC1 [#12, #23]. Beyond DSB repair, RAD50 participates in telomere length control via MRN/ATM regulation of TRF1 [#17] and, in the cytoplasm, interacts with CARD9 to couple cytosolic dsDNA sensing to NF-\\u03baB activation and pro-IL-1\\u03b2 production [#26].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Established that human RAD50 is the homolog of yeast Rad50 and acts within a multiprotein complex rather than alone, defining the molecular context for all subsequent mechanism.\",\n      \"evidence\": \"Co-immunoprecipitation and cDNA characterization identifying stable RAD50-MRE11 association\",\n      \"pmids\": [\"8756642\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the third subunit\", \"No enzymatic or structural mechanism\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Identified NBS1 as the third MRN subunit and connected the complex to a human genome-instability disease, linking DSB repair to checkpoint signaling.\",\n      \"evidence\": \"Gene mapping and immunofluorescence in NBS patient cells showing NBS1 dependence of RAD50/MRE11 IR foci\",\n      \"pmids\": [\"9590181\", \"9315668\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of foci assembly not resolved\", \"Catalytic roles of each subunit unknown\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Assigned enzymatic functions within the reconstituted complex, showing RAD50 provides ATP binding that switches MRE11 nuclease specificity.\",\n      \"evidence\": \"Biochemical reconstitution with recombinant NBS1/MRE11/RAD50, nuclease and helicase assays with mutants\",\n      \"pmids\": [\"10346816\", \"11454871\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the ATP switch not yet visualized\", \"In vivo relevance of ATP-controlled specificity not tested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Resolved the structural architecture: RAD50 is an ABC-ATPase whose coiled coils end in a Zn2+ zinc-hook dimer interface enabling long-range DNA tethering.\",\n      \"evidence\": \"X-ray crystallography of archaeal Rad50/Mre11, EM, and yeast genetics of zinc-hook mutants\",\n      \"pmids\": [\"11371344\", \"12152085\", \"14698290\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How hook signal propagates to the catalytic head not yet shown\", \"Eukaryotic full-complex architecture unresolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstrated that MRN directly activates ATM kinase, establishing RAD50's complex as an upstream signaling activator and not merely a repair enzyme.\",\n      \"evidence\": \"In vitro kinase assays with recombinant MRN and ATM substrates p53, Chk2, H2AX\",\n      \"pmids\": [\"15064416\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not separate tethering from direct activation contributions\", \"RAD50-specific contribution to ATM activation not isolated\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Visualized the DNA-induced conformational change that converts intracomplex coiled-coil interactions to intercomplex tethering, providing a physical mechanism for end bridging.\",\n      \"evidence\": \"Atomic force and electron microscopy and single-molecule imaging of hRAD50/MRE11/NBS1 on DNA\",\n      \"pmids\": [\"16163361\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Coupling to ATP cycle quantitative detail incomplete\", \"Nuclease activation step not captured\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Clarified that MRN promotes ATM activation in two steps, with RAD50-mediated DNA tethering increasing local ATM concentration to drive monomer conversion.\",\n      \"evidence\": \"Reconstitution in Xenopus cell-free extracts with NBS1 ATM-binding-domain mutants\",\n      \"pmids\": [\"16622404\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"RAD50 ATPase-state requirement not directly tested here\", \"In-cell ordering of steps not established\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defined the ATP-driven molecular switch at atomic resolution and tied RAD50 Ser-635 ATM phosphorylation to downstream checkpoint signaling.\",\n      \"evidence\": \"Mre11-Rad50-ATP\\u03b3S crystal structure with biochemistry; phosphosite mapping and S635G complementation in RAD50-deficient cells\",\n      \"pmids\": [\"21511873\", \"22102415\", \"21757780\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinetics of the endo-to-exo transition in vivo not measured\", \"S635 effector pathway beyond SMC1 incompletely mapped\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showed RAD50 ATPase activity directly powers DNA-end unwinding required for resection, linking the catalytic cycle to repair output in human cells.\",\n      \"evidence\": \"Single-molecule FRET unwinding assays with RAD50 catalytic mutants plus cellular repair assays\",\n      \"pmids\": [\"24191051\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Coupling of unwinding to nucleolytic incision not fully resolved\", \"Role of accessory factors during unwinding not addressed\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Established the structural separation between the closed-state tethering/signaling function and hydrolysis-driven opening required for resection, and revealed a cytoplasmic RAD50-CARD9 innate-immune role.\",\n      \"evidence\": \"Structure-based Rad50 mutants across organisms; RAD50-CARD9 Co-IP and conditional-knockout cytokine and infection assays\",\n      \"pmids\": [\"24493214\", \"24777530\", \"24694934\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of RAD50-CARD9 interaction unknown\", \"Crosstalk between nuclear repair and cytoplasmic immune roles unexplored\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated that both RAD50 ATPase sites are jointly required for adduct cleavage and ATM activation, and that RAD50 enables MRN to translocate on DNA and load EXO1 for processive resection.\",\n      \"evidence\": \"Single-active-site Rad50 dimer mutants in ATPase/nuclease/ATM assays; single-molecule microscopy of MRN-EXO1 on DNA\",\n      \"pmids\": [\"28369545\", \"28867292\", \"28134932\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Coordination of the two active sites in vivo not directly observed\", \"Adduct-specificity determinants incompletely defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Resolved the conformational mechanics of DNA clamping and nuclease loading and identified C1QBP as a phosphorylation-controlled negative regulator of MRE11/RAD50 nuclease.\",\n      \"evidence\": \"Cryo-EM of SbcCD resting and DNA-bound states; Co-IP, nuclease, and ATM-phosphosite analysis of the C1QBP-MRE11-RAD50 complex\",\n      \"pmids\": [\"31492634\", \"31353207\", \"30819891\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Eukaryotic full-complex conformational cycle not yet at high resolution\", \"Regulation of C1QBP dissociation timing in cells incomplete\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Delivered near-complete eukaryotic MRN architecture and RAD50-mediated higher-order oligomerization, explaining how RAD50 orients MRE11 for distinct endo- versus exonucleolytic cuts and bridges paired complexes.\",\n      \"evidence\": \"Cryo-EM of C. thermophilum MRN and SbcCD on diverse substrates; EM and yeast genetics of Rad50 oligomerization mutants\",\n      \"pmids\": [\"36577401\", \"35987200\", \"35501303\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional role of MRN-MRN dimerization in cells incompletely defined\", \"Mechanism converting orientation to substrate selection not fully resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How RAD50's nuclear DSB-processing functions are coordinated with its cytoplasmic innate-immune signaling role, and the structural basis of RAD50-CARD9 dsDNA sensing, remain open.\",\n      \"evidence\": \"No reconstitution or structural study in the timeline connecting the two compartmental roles\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of the dsDNA-RAD50-CARD9 complex\", \"No mechanism partitioning RAD50 between nucleus and cytoplasm\", \"Disease-causing RAD50 mutation effects on either role not characterized in this corpus\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [4, 11, 22, 24, 27, 35]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [15, 32, 33]},\n      {\"term_id\": \"GO:0140097\", \"supporting_discovery_ids\": [4, 7, 31, 33, 39]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [4, 7, 22, 24, 31]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [6, 9, 15, 42]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [18]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 2, 8]},\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [1, 14]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [26]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [5, 17]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [0, 2, 4, 31, 33]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [12, 16, 23, 27]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [13, 28]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [26]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [5, 17]}\n    ],\n    \"complexes\": [\n      \"MRN complex (MRE11-RAD50-NBS1)\",\n      \"MRX complex (Mre11-Rad50-Xrs2)\",\n      \"MRC complex (MRE11-RAD50-C1QBP)\"\n    ],\n    \"partners\": [\n      \"MRE11\",\n      \"NBS1\",\n      \"BRCA1\",\n      \"CtIP\",\n      \"EXO1\",\n      \"C1QBP\",\n      \"CARD9\",\n      \"RINT-1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}