{"gene":"SMC6","run_date":"2026-06-10T07:46:35","timeline":{"discoveries":[{"year":2003,"finding":"SMC6 forms a high-molecular-mass complex with SMC5 and the non-SMC subunit NSE1 (identified by mass spectrometry after purification of fission yeast Smc5), establishing the core composition of the Smc5-6 complex required for DNA repair and proliferation.","method":"Affinity purification and mass spectrometry; co-immunoprecipitation; genetic epistasis with Rhp51","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP, MS identification, genetic epistasis, replicated across organisms","pmids":["12966087"],"is_preprint":false},{"year":2003,"finding":"NSE1 and NSE2 are essential non-SMC subunits of the fission yeast Smc5-6 complex that interact with Smc5 in vivo; loss of Nse1 or Nse2 produces phenotypes identical to Smc5-6 inactivation, and epistasis places them in the same homologous-recombination DSB repair pathway as Rhp51.","method":"Affinity purification/mass spectrometry, co-IP, genetic epistasis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — co-IP confirmed subunit membership, epistasis defined pathway, replicated across labs","pmids":["12966087"],"is_preprint":false},{"year":2004,"finding":"NSE3 is an additional essential non-SMC subunit of the fission yeast Smc5-6 complex; it is required for mitotic chromosome segregation, resistance to genotoxic agents, and meiotic recombination-based DNA repair in a pathway epistatic to Rhp51.","method":"Biochemical purification, genetic epistasis, co-immunoprecipitation","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — biochemical isolation plus epistasis, replicated in two SMC5/6 subunit studies","pmids":["15331764"],"is_preprint":false},{"year":2004,"finding":"The Smc5/6 complex is required for coordinated DNA damage response: fission yeast cells lacking functional Smc6 initiate a normal Chk1 checkpoint but then enter lethal mitosis, indicating Smc5/6 is needed to maintain checkpoint arrest through ongoing DNA repair rather than for checkpoint initiation.","method":"Genetic loss-of-function (smc6 and nse1 mutants), checkpoint kinase phosphorylation assays, live-cell phenotyping","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with defined cellular phenotype, single lab, two readouts (Chk1 phosphorylation + lethal mitosis)","pmids":["14701739"],"is_preprint":false},{"year":2004,"finding":"Rad62 physically associates with the Smc5-6 complex and is required for recombinational repair of DSBs and recovery from stalled replication; its DNA repair role is epistatic with rhp51 and genetically interacts with rad60 and smc6.","method":"Co-immunoprecipitation, genetic epistasis, sensitivity assays","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus epistasis, single lab","pmids":["15485909"],"is_preprint":false},{"year":2004,"finding":"SMC6 is required for MMS-induced sister chromatid recombination and interchromosomal recombination in budding yeast; smc6-56 rad52 double mutants show MMS sensitivity similar to rad52 alone, placing Smc6 in the Rad52-dependent recombination pathway.","method":"Temperature-sensitive smc6 mutants, genetic epistasis with rad52, recombination assays","journal":"DNA repair","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis with two orthogonal readouts (sensitivity + recombination frequency), single lab","pmids":["15010319"],"is_preprint":false},{"year":2005,"finding":"Smc5 and Smc6 are enriched at rDNA and telomeres; conditional smc5-6 and smc6-9 mutants show impaired segregation of repetitive chromosomal regions, accumulation of Holliday junctions at rDNA, and RAD9-dependent Rad53 activation; deletion of RAD52 partially suppresses temperature sensitivity, indicating the complex prevents sister chromatid junctions at repetitive loci.","method":"ChIP, 2D gel electrophoresis (Holliday junction detection), genetic epistasis, conditional mutants","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — ChIP localization + 2D gel biochemistry + epistasis, multiple orthogonal methods in one rigorous study","pmids":["15793567"],"is_preprint":false},{"year":2006,"finding":"NSE1 and NSE2 (with NSE3-NSE4) form a subcomplex within the Smc5-6 holocomplex; NSE4 is identified as the kleisin component that bridges the Smc5 and Smc6 head domains, with its C-terminal region interacting with the Smc5 head and a predicted winged-helix motif required for this interaction.","method":"Co-immunoprecipitation, yeast two-hybrid, in vitro binding with purified recombinant proteins, domain mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with mutagenesis, structural prediction validated biochemically, single lab","pmids":["17005570"],"is_preprint":false},{"year":2006,"finding":"Nse5 and Nse6 form a distinct heterodimeric subcomplex within the Smc5-6 holocomplex; Nse5/6 mutants display high spontaneous DNA damage and are required for tolerance of UV lesions and stabilization/processing of stalled replication forks; their UV sensitivity is suppressed by deletion of Rad51 homolog Rhp51, and viability requires Mus81 and Rqh1, implicating Nse5/6 in suppressing aberrant recombination at replication forks.","method":"Genetic epistasis, sensitivity assays, RusA rescue experiment","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic epistasis with multiple suppressors, single lab","pmids":["16478984"],"is_preprint":false},{"year":2006,"finding":"The Smc5-Smc6 complex is recruited de novo to DSBs and is essential for repair by homologous recombination between sister chromatids (SCR), and suppresses gross chromosomal rearrangements by preventing non-sister recombination events.","method":"Chromatin immunoprecipitation (ChIP) at induced DSBs, genetic epistasis, GCR assays","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — ChIP demonstrating recruitment + GCR assays + genetic epistasis, replicated across studies","pmids":["16892052"],"is_preprint":false},{"year":2007,"finding":"Smc5-Smc6 and Mre11 complexes mediate the nucleolar exclusion of Rad52 recombination foci at rDNA DSBs; this exclusion depends on SUMO modification of Rad52. Failure of this pathway leads to Rad52 foci within the nucleolus, rDNA hyperrecombination, and excision of extrachromosomal rDNA circles.","method":"Live fluorescence microscopy, SUMO modification assays, genetic epistasis","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct imaging of relocalization + biochemical SUMO modification + genetic rescue, multiple orthogonal methods","pmids":["17643116"],"is_preprint":false},{"year":2007,"finding":"Nse1, a subunit of the Smc5-Smc6 complex, is required for Rad52-dependent post-replication repair (PRR) of UV-damaged DNA; genetic analysis implicates both the Nse1 ubiquitin-ligase-like activity and the Mms21 SUMO-ligase activity of the complex in this Rad52-dependent repair mode.","method":"Genetic epistasis, UV sensitivity assays, allele-specific mutant analysis","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis with multiple alleles, single lab","pmids":["17923688"],"is_preprint":false},{"year":2008,"finding":"The Nse1 RING-like domain supports Smc5-Smc6 holocomplex integrity: it is required for normal Nse1-Nse3-Nse4 trimer formation in vitro and for damage-induced recruitment of Nse4 and Smc5 to subnuclear foci in vivo. No ubiquitin E3 ligase activity was detected for full-length or isolated Nse1 RING domain in vitro.","method":"In vitro ubiquitin ligase assay, co-IP, in vivo focus formation (immunofluorescence), mutagenesis","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro reconstitution (negative result for ligase) + co-IP + live imaging, single lab","pmids":["18667531"],"is_preprint":false},{"year":2008,"finding":"The smc6-9 mutation increases translocation-class gross chromosomal rearrangements (GCRs) in a manner dependent on break-induced replication (BIR) and independent of NHEJ; translocations cluster near repetitive sequences, showing that Smc5-Smc6 suppresses GCR formation by reducing DNA damage at repetitive loci.","method":"GCR assay, genetic epistasis (BIR and NHEJ mutants), genome sequencing of rearrangements","journal":"DNA repair","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with defined pathway, single lab","pmids":["18585101"],"is_preprint":false},{"year":2009,"finding":"The Nse5-Nse6 heterodimer interacts with the hinge regions of both Smc5 and Smc6, while the Nse1-Nse3-Nse4 subcomplex binds to the head and adjacent coiled-coil of Smc5, and Nse2 binds the middle coiled-coil of Smc5; these three entities occupy distinct sites defining the Smc5/6 complex architecture.","method":"Yeast two-hybrid, in vitro binding with purified recombinant proteins","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with purified recombinants + two-hybrid, multiple subunit interactions mapped, single lab","pmids":["19141609"],"is_preprint":false},{"year":2009,"finding":"In smc6 mutants after DNA damage, chromosome arm segregation fails due to aberrant persistence of cohesin that is normally removed by the Separase-independent pathway; overexpression of Separase bypasses this defect and restores viability, identifying defective cohesin removal as a major determinant of mitotic lethality in Smc5-Smc6 mutants.","method":"Genetic epistasis, cohesin persistence assays, Separase overexpression rescue","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic rescue with Separase + cohesin persistence biochemistry + epistasis with topoisomerase II mutant, multiple orthogonal approaches","pmids":["19528228"],"is_preprint":false},{"year":2011,"finding":"Smc5 binds strongly and specifically to single-stranded DNA (ssDNA) as a monomer independently of Smc6; this binding is regulated by ATP and is observed with ssDNA of ~60 nt or longer, consistent with substrates generated during DNA replication and repair.","method":"In vitro DNA-binding assay with purified recombinant Smc5, ATPase mutagenesis, EMSA","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro biochemistry with purified protein + ATPase mutagenesis, single lab","pmids":["21293191"],"is_preprint":false},{"year":2011,"finding":"Smc6 is a strong DNA-binding protein with preference for single-stranded DNA; it binds DNA independently of other Smc5-6 complex components and its activity is modulated by nucleotides; the minimal ssDNA size for tight association is ~60 nucleotides.","method":"In vitro DNA-binding assay with purified recombinant Smc6, EMSA","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro biochemistry with purified protein, single lab","pmids":["22086171"],"is_preprint":false},{"year":2011,"finding":"In meiosis, the Smc5-Smc6 complex is required for removing chromosome linkages (including those independent of Spo11-induced recombination) to allow proper chromosome segregation; the complex localizes to specific chromosome regions during meiotic prophase I.","method":"Immunofluorescence localization, genetic (spo11 epistasis), chromosome segregation assays","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization + epistasis, single lab","pmids":["21731634"],"is_preprint":false},{"year":2012,"finding":"Smc6 mutation leads to accumulation of recombination intermediates at centromeres (assayed by 2D gel) and increased centromere-associated Rad52 foci; a rad52 mutation suppressing centromeric Rad52 foci also suppresses nocodazole sensitivity of smc6 mutants, showing that Smc5-Smc6 regulates recombination at centromeric loci. The SUMO ligase subunit of Smc5-Smc6 (Mms21) also promotes sumoylation of kinetochore proteins and affects mitotic spindles.","method":"2D gel electrophoresis, fluorescence microscopy (Rad52 foci co-localization), SUMO modification assays, genetic epistasis","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — 2D gel + imaging + biochemical SUMO assay, single lab","pmids":["23284708"],"is_preprint":false},{"year":2012,"finding":"Nse5-Nse6 of the Smc5-Smc6 complex is required for meiotic resolution of Holliday junction-like recombination intermediates (DNA joint molecules) via promotion of Mus81-Eme1 endonuclease activity; RusA bacterial resolvase partially rescues nse6Δ meiotic defects, and elimination of Rec12 (Spo11) nearly completely rescues defects, placing Nse5-Nse6 after DSB formation in the meiotic recombination pathway.","method":"Southern blotting for DNA joint molecules, RusA rescue, genetic epistasis (rec12Δ, mus81Δ)","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Strong — biochemical joint molecule detection + genetic rescue + epistasis, multiple orthogonal methods","pmids":["22855558"],"is_preprint":false},{"year":2013,"finding":"SMC6 is an essential gene in mice (complete knockout causes early embryonic lethality); a hypomorphic ATPase domain mutation (S994A) results in viable mice with sensitivity to induction of sister chromatid exchanges by UV and mitomycin C, and accumulation of oxidative damage, but not sensitivity to killing by DNA-damaging agents.","method":"Gene knockout, ATPase point mutant knockin, sister chromatid exchange assay, embryonic fibroblast sensitivity assays","journal":"DNA repair","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout lethality + ATPase mutagenesis in mammals + multiple cellular assays, replicated internally","pmids":["23518413"],"is_preprint":false},{"year":2013,"finding":"During mouse spermatogenesis, Smc6 localizes to pericentromeric heterochromatin domains specifically when differentiating spermatogonia commit irreversibly toward meiosis; Smc6-negative meiotic cells fail to complete the first meiotic division; DNA repair/recombination sites (γH2AX, Rad51) do not co-localize with the Smc6-positive pericentromeric domains.","method":"Immunofluorescence/localization in testis sections, co-localization analysis, meiotic staging","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization in mammalian tissue with meiotic phenotype, single lab","pmids":["23907463"],"is_preprint":false},{"year":2013,"finding":"In Drosophila, SMC6 (CG5524) mutants are hypersensitive to genotoxic agents (ionizing radiation, camptothecin, hydroxyurea, MMS); MAGE physically interacts with Drosophila Nse homologs, indicating conservation of the SMC5/6 complex structure; caffeine-induced apoptosis in smc6 mutants is suppressed by Rad51 depletion, placing SMC6 in a homologous recombination repair pathway.","method":"Genetic screen, genotoxin sensitivity assays, co-immunoprecipitation, genetic epistasis (Rad51 depletion)","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP + genetic epistasis, replicated in model organism","pmids":["23555814"],"is_preprint":false},{"year":2015,"finding":"The Smc5-Smc6 heterodimer contains two independent DNA-binding domains (DBDs) in each SMC subunit: one in the hinge/coiled-coil region and one in the ATPase head domain; heterodimerization of full-length proteins specifically increases affinity for double-stranded DNA substrates compared to monomers.","method":"In vitro DNA-binding assays with purified recombinant domain fragments, EMSA","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro domain mapping with recombinant proteins, single lab","pmids":["25984708"],"is_preprint":false},{"year":2019,"finding":"Brc1 (fission yeast) is required for the focal accumulation (foci formation) of the Smc5-Smc6 complex during replication stress and for activation of its intrinsic SUMO ligase activity at collapsed replication forks; the Nse5-Nse6 heterodimer is required for chromatin association and SUMO ligase activity of Smc5-Smc6; Brc1 interacts physically with Nse5-Nse6 and with γ-H2A, thereby tethering Smc5-Smc6 at replicative DNA lesions.","method":"Co-immunoprecipitation, SUMO ligase activity assay, immunofluorescence focus formation, genetic epistasis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — co-IP + enzymatic assay + imaging, multiple orthogonal methods in single study","pmids":["30348841"],"is_preprint":false},{"year":2026,"finding":"The human SMC5/6 complex is recruited to transcription-replication conflicts (TRCs) in response to DNA supercoiling buildup in SETX-deficient cells; once recruited, SMC5/6 facilitates recruitment of the BLM/TOP3A/RMI1/RMI2 (BTRR) complex, which resolves TRCs in a TOP3A catalytic-activity-dependent manner; BTRR in turn recruits FANCM to activate the FANCD2 pathway, defining the SMC5/6-BTRR-FANCM-FANCD2 axis.","method":"Synthetic lethality screen, ChIP/proximity ligation for recruitment, epistasis with TOP3A catalytic mutant, co-immunoprecipitation","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Strong — synthetic lethality + co-IP + catalytic mutant epistasis, multiple orthogonal methods in single study on human cells","pmids":["41533569"],"is_preprint":false},{"year":2025,"finding":"Cryo-EM structure of the human HBx-CRL4-SMC5/6 complex at 3.1 Å resolution reveals that HBx adopts a zinc-stabilized Y-shaped architecture and directly contacts the SMC6 subunit via a conserved 'Leucine Key' motif (LRCKL) on SMC6 that fits into a helix-turn-helix (HTH) pocket on HBx; disrupting this interface with Tranilast suppresses HBV replication.","method":"Cryo-electron microscopy (3.1 Å), reconstitution of ten-subunit complex, molecular docking, biochemical validation, HBV replication assay","journal":"bioRxiv","confidence":"High","confidence_rationale":"Tier 1 / Moderate — cryo-EM structure + reconstitution + biochemical validation + functional assay, single preprint study","pmids":[],"is_preprint":true},{"year":2025,"finding":"SMC5/6-mediated repression of extrachromosomal circular/plasmid DNA transcription depends exclusively on the SIMC1-SLF2 subcomplex (the human counterpart of yeast Nse5/6) and requires a conserved SIMC1-SLF2–SMC6 interaction; SLF1/2 is dispensable for plasmid silencing; plasmid silencing requires the SUMO pathway but not PML nuclear bodies.","method":"Reporter-based transcriptional silencing assay, co-immunoprecipitation, genetic knockdown/knockout","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP + functional transcriptional assay, single preprint lab","pmids":[],"is_preprint":true}],"current_model":"SMC6 is a core ATPase subunit of the conserved SMC5/6 complex that binds single-stranded and double-stranded DNA through hinge and head-domain DBDs, is recruited de novo to DSBs, stalled replication forks, and transcription-replication conflicts, where it promotes sister-chromatid recombination, prevents accumulation of aberrant Holliday junctions at repetitive loci, and facilitates Separase-independent cohesin removal to ensure chromosome segregation; the complex achieves these functions through its associated SUMO ligase (Mms21/NSE2), its Nse5/6 (or human SIMC1-SLF2) regulatory subcomplex that controls chromatin loading and SUMO ligase activation, and an SMC5/6-BTRR-FANCM-FANCD2 axis that resolves transcription-replication conflicts, while the SMC6 subunit itself is directly targeted for degradation by viral proteins (HBx) that bind the SMC6 'Leucine Key' motif to counteract restriction of viral episomes."},"narrative":{"mechanistic_narrative":"SMC6 is a core ATPase subunit of the conserved SMC5/6 complex that governs the recombinational repair and segregation of damaged and repetitive chromosomes [PMID:12966087, PMID:16892052]. Together with SMC5 it forms the structural heterodimer of a holocomplex that incorporates the essential non-SMC subunits NSE1, NSE2, NSE3, and the NSE4 kleisin bridging the two SMC head domains, plus the NSE5/NSE6 heterodimer that contacts the SMC hinges [PMID:12966087, PMID:15331764, PMID:17005570, PMID:19141609]. SMC6 itself is a strong, nucleotide-modulated DNA-binding protein with two independent DNA-binding domains — one in the hinge/coiled-coil region and one in the ATPase head — that prefer single-stranded DNA as monomers but gain double-stranded DNA affinity upon heterodimerization with SMC5 [PMID:21293191, PMID:22086171, PMID:25984708]. The complex is recruited de novo to double-strand breaks and is essential for homologous recombination between sister chromatids while suppressing non-sister recombination and gross chromosomal rearrangements, particularly at repetitive loci such as rDNA, telomeres, and centromeres where it prevents accumulation of aberrant Holliday-junction intermediates [PMID:15793567, PMID:16892052, PMID:18585101, PMID:23284708]. At collapsed replication forks SMC5/6 is tethered through an NSE5/6–Brc1–γ-H2A interaction that licenses its chromatin association and intrinsic SUMO ligase activity [PMID:30348841], and in human cells it is recruited to transcription–replication conflicts where it nucleates a BTRR–FANCM–FANCD2 resolution axis [PMID:41533569]. SMC6 function ensures faithful chromosome segregation by enabling Separase-independent cohesin removal after DNA damage [PMID:19528228] and is required during meiosis to remove chromosome linkages [PMID:21731634, PMID:22855558]. SMC6 is essential in mice, with ATPase-domain integrity required to limit damage-induced sister chromatid exchange and oxidative damage [PMID:23518413]. The SMC6 subunit is directly targeted by the hepatitis B virus protein HBx, which engages a conserved 'Leucine Key' (LRCKL) motif on SMC6 to neutralize its restriction of viral episomal DNA.","teleology":[{"year":2003,"claim":"Established the core subunit composition of the SMC5/6 complex, defining SMC6 as part of a multi-subunit machine rather than a standalone factor and placing it in a Rhp51-dependent DNA repair pathway.","evidence":"Affinity purification/mass spectrometry, co-IP, and genetic epistasis in fission yeast","pmids":["12966087"],"confidence":"High","gaps":["Stoichiometry and architecture of subunit contacts not yet resolved","Biochemical activity of the complex undefined"]},{"year":2004,"claim":"Identified NSE3 as an additional essential non-SMC subunit and showed SMC5/6 is required to sustain checkpoint-coupled repair — cells initiate Chk1 but enter lethal mitosis — distinguishing a repair/maintenance role from checkpoint initiation.","evidence":"Biochemical purification, checkpoint kinase phosphorylation assays, and live-cell phenotyping in fission yeast","pmids":["15331764","14701739","15485909"],"confidence":"Medium","gaps":["Molecular mechanism by which the complex maintains arrest not defined","Direct DNA substrate not identified"]},{"year":2004,"claim":"Placed SMC6 directly in the Rad52/Rad51-dependent recombination pathway by showing it is required for MMS-induced sister chromatid and interchromosomal recombination.","evidence":"Temperature-sensitive smc6 mutants with epistasis to rad52 and recombination assays in budding yeast","pmids":["15010319"],"confidence":"Medium","gaps":["Whether SMC5/6 acts before or after strand invasion unresolved","No biochemical reconstitution of its recombination role"]},{"year":2005,"claim":"Localized SMC5/6 to rDNA and telomeres and demonstrated it prevents accumulation of Holliday junctions at repetitive loci, explaining its role in segregating repetitive chromosomal regions.","evidence":"ChIP, 2D-gel Holliday junction detection, and genetic epistasis in conditional mutants","pmids":["15793567"],"confidence":"High","gaps":["Mechanism by which junctions are prevented vs resolved not separated","Direct enzymatic activity on junctions not shown"]},{"year":2006,"claim":"Resolved the internal architecture of the complex, identifying NSE4 as the kleisin bridging SMC5 and SMC6 heads, and defining NSE5/6 as a distinct hinge-associated subcomplex required for replication fork stability.","evidence":"In vitro binding with recombinant proteins, yeast two-hybrid, domain mutagenesis, and genetic epistasis","pmids":["17005570","16478984","16892052"],"confidence":"High","gaps":["How head-bridging kleisin couples to ATPase cycle unknown","Functional consequence of hinge-head geometry on DNA handling unclear"]},{"year":2007,"claim":"Linked SMC5/6 to SUMO-dependent spatial control of recombination by showing it excludes Rad52 foci from the nucleolus to prevent rDNA hyperrecombination, and connected NSE1 and the Mms21 SUMO ligase to Rad52-dependent post-replication repair.","evidence":"Live fluorescence microscopy, SUMO modification assays, and allele-specific genetic analysis","pmids":["17643116","17923688"],"confidence":"High","gaps":["SUMO substrates driving exclusion not fully enumerated","Mechanism connecting NSE1 RING to repair undefined"]},{"year":2008,"claim":"Clarified that the NSE1 RING-like domain supports holocomplex integrity and damage-induced focus recruitment rather than acting as a detectable ubiquitin ligase, refining the functional assignment of complex subunits.","evidence":"In vitro ubiquitin ligase assays (negative), co-IP, in vivo focus formation, and mutagenesis; plus GCR assays showing BIR-dependent translocation suppression","pmids":["18667531","18585101"],"confidence":"Medium","gaps":["Whether NSE1 has E3 activity in a different context unresolved","Substrate of any associated ligase not identified here"]},{"year":2009,"claim":"Mapped the spatial organization of all subcomplexes onto SMC5/6 (NSE5/6 at hinges, NSE1-3-4 at SMC5 head, NSE2 at middle coiled-coil) and revealed that mitotic lethality of smc6 mutants arises from failed Separase-independent cohesin removal.","evidence":"Yeast two-hybrid and in vitro binding for architecture; Separase overexpression rescue and cohesin persistence assays for segregation","pmids":["19141609","19528228"],"confidence":"High","gaps":["Molecular mechanism linking SMC5/6 to cohesin removal undefined","How architecture supports cohesin function not established"]},{"year":2011,"claim":"Defined the biochemical DNA-binding behaviour of SMC6 and SMC5, showing each is a strong, nucleotide-modulated, ssDNA-preferring binder as a monomer, consistent with engaging replication/repair intermediates.","evidence":"In vitro EMSA DNA-binding assays with purified recombinant SMC5 and SMC6 and ATPase mutagenesis","pmids":["21293191","22086171"],"confidence":"Medium","gaps":["Physiological DNA substrate not confirmed in vivo","Coupling of binding to ATPase cycle not resolved"]},{"year":2011,"claim":"Extended SMC5/6 function into meiosis, showing it removes chromosome linkages including Spo11-independent ones to permit segregation, and localizes to specific prophase chromosome regions.","evidence":"Immunofluorescence localization, spo11 epistasis, and chromosome segregation assays","pmids":["21731634"],"confidence":"Medium","gaps":["Nature of the removed linkages unclear","Mechanism of region-specific localization unknown"]},{"year":2012,"claim":"Showed SMC5/6 regulates recombination at centromeres and that its Mms21 SUMO ligase sumoylates kinetochore proteins, and established that NSE5/6 promotes meiotic resolution of joint molecules via Mus81-Eme1.","evidence":"2D gels for recombination intermediates, Rad52 foci imaging, SUMO assays, Southern blotting for joint molecules, RusA rescue, and epistasis","pmids":["23284708","22855558"],"confidence":"Medium","gaps":["Direct kinetochore SUMO targets not fully validated","How NSE5/6 stimulates Mus81-Eme1 mechanistically unknown"]},{"year":2013,"claim":"Established SMC6 as essential in a mammal and tied ATPase integrity to suppression of sister chromatid exchange and oxidative damage, while documenting conservation of complex structure and HR function across Drosophila and mouse spermatogenesis.","evidence":"Mouse knockout, ATPase S994A knockin, sister chromatid exchange assays, immunofluorescence in testis, Drosophila genotoxin sensitivity and co-IP","pmids":["23518413","23907463","23555814"],"confidence":"High","gaps":["Embryonic-lethal step in knockout not defined","Role of pericentromeric SMC6 localization in meiotic commitment unclear"]},{"year":2015,"claim":"Resolved the DNA-binding module organization, demonstrating two independent DBDs per SMC subunit (hinge/coiled-coil and ATPase head) and that heterodimerization increases dsDNA affinity, providing a structural basis for substrate engagement.","evidence":"In vitro EMSA with purified recombinant domain fragments","pmids":["25984708"],"confidence":"Medium","gaps":["In vivo contribution of each DBD not dissected","How DNA binding is coordinated with ATP hydrolysis unknown"]},{"year":2019,"claim":"Defined the recruitment logic at collapsed replication forks: Brc1 bridges NSE5/6 and γ-H2A to tether SMC5/6 and activate its intrinsic SUMO ligase, explaining how the complex is targeted to replicative lesions.","evidence":"Co-IP, SUMO ligase activity assays, focus-formation imaging, and genetic epistasis in fission yeast","pmids":["30348841"],"confidence":"High","gaps":["Human counterpart of this tether not addressed here","SUMO ligase substrates at forks not enumerated"]},{"year":2026,"claim":"Placed human SMC5/6 at the head of a transcription-replication conflict resolution axis, showing it recruits the BTRR complex (resolving via TOP3A catalysis) which then recruits FANCM to activate FANCD2.","evidence":"Synthetic lethality screen, ChIP/proximity ligation, TOP3A catalytic-mutant epistasis, and co-IP in human cells","pmids":["41533569"],"confidence":"High","gaps":["How SMC5/6 senses supercoiling buildup not defined","Direct SMC6–BTRR contacts not mapped structurally"]},{"year":2025,"claim":"Defined the human regulatory subcomplex and viral antagonism interface: SIMC1-SLF2 (the Nse5/6 counterpart) is required for SMC5/6-mediated silencing of extrachromosomal DNA, and HBx engages a conserved SMC6 'Leucine Key' motif to counteract this restriction.","evidence":"Cryo-EM of the HBx-CRL4-SMC5/6 complex (preprint), reconstitution, reporter silencing assays, co-IP, and HBV replication assays","pmids":[],"confidence":"Medium","gaps":["Both reports are single-lab preprints awaiting peer review","Mechanism by which SIMC1-SLF2–SMC6 contact drives transcriptional silencing not defined","How SUMO pathway dependence connects to silencing unclear"]},{"year":null,"claim":"How the SMC6 ATPase cycle, its two DNA-binding domains, and SUMO ligase activation are mechanically coupled to discriminate and resolve recombination intermediates at distinct genomic loci remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No integrated structure-function model linking ATP hydrolysis to DNA loop/junction handling","Direct enzymatic activity of the complex on Holliday junctions not demonstrated","Full SUMO substrate landscape across loci undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[16,21]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[16,17,24]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,7,14]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[9,12,25]},{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[6,10]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[6,19,22]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[9,5,6]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[15,18]},{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[8,25,26]}],"complexes":["SMC5/6 complex","NSE1-NSE3-NSE4 subcomplex","NSE5/NSE6 (SIMC1-SLF2) subcomplex"],"partners":["SMC5","NSE1","NSE2","NSE3","NSE4","NSE5","NSE6","HBX"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96SB8","full_name":"Structural maintenance of chromosomes protein 6","aliases":[],"length_aa":1091,"mass_kda":126.3,"function":"Core component of the SMC5-SMC6 complex, a complex involved in DNA double-strand breaks by homologous recombination. The complex may promote sister chromatid homologous recombination by recruiting the SMC1-SMC3 cohesin complex to double-strand breaks. The complex is required for telomere maintenance via recombination in ALT (alternative lengthening of telomeres) cell lines and mediates sumoylation of shelterin complex (telosome) components which is proposed to lead to shelterin complex disassembly in ALT-associated PML bodies (APBs). Required for recruitment of telomeres to PML nuclear bodies. SMC5-SMC6 complex may prevent transcription of episomal DNA, such as circular viral DNA genome (PubMed:26983541)","subcellular_location":"Nucleus; Nucleus speckle; Chromosome; Nucleus, PML body; Chromosome, telomere","url":"https://www.uniprot.org/uniprotkb/Q96SB8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/SMC6","classification":"Common Essential","n_dependent_lines":730,"n_total_lines":1208,"dependency_fraction":0.6043046357615894},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SMC6","total_profiled":1310},"omim":[{"mim_id":"620184","title":"ATELIS SYNDROME 1; ATELS1","url":"https://www.omim.org/entry/620184"},{"mim_id":"618467","title":"SMC5-SMC6 COMPLEX LOCALIZATION FACTOR 1; SLF1","url":"https://www.omim.org/entry/618467"},{"mim_id":"617263","title":"NSE1 HOMOLOG, SMC5-SMC6 COMPLEX COMPONENT; NSMCE1","url":"https://www.omim.org/entry/617263"},{"mim_id":"617246","title":"NSE2 (MMS21) HOMOLOG, SMC5-SMC6 COMPLEX SUMO LIGASE; NSMCE2","url":"https://www.omim.org/entry/617246"},{"mim_id":"617241","title":"LUNG DISEASE, IMMUNODEFICIENCY, AND CHROMOSOME BREAKAGE SYNDROME; LICS","url":"https://www.omim.org/entry/617241"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SMC6"},"hgnc":{"alias_symbol":["FLJ22116"],"prev_symbol":["SMC6L1"]},"alphafold":{"accession":"Q96SB8","domains":[{"cath_id":"3.40.50.300","chopping":"48-202_986-1067","consensus_level":"medium","plddt":84.6727,"start":48,"end":1067}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96SB8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96SB8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96SB8-F1-predicted_aligned_error_v6.png","plddt_mean":80.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SMC6","jax_strain_url":"https://www.jax.org/strain/search?query=SMC6"},"sequence":{"accession":"Q96SB8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96SB8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96SB8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96SB8"}},"corpus_meta":[{"pmid":"17643116","id":"PMC_17643116","title":"The Smc5-Smc6 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Antagonized by the SV40 Large T Antigen","date":"2025-03-30","source":"bioRxiv","url":"https://doi.org/10.1101/2025.03.27.645818","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.05.11.653314","title":"<i>Ureaplasma parvum</i>  SMC-ScpAB complex is capable of loop extrusion and demonstrates properties that distinguish it from  <i>Bacillus subtilis</i>  homologue","date":"2025-05-12","source":"bioRxiv","url":"https://doi.org/10.1101/2025.05.11.653314","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.10.28.620692","title":"Conserved yet Divergent Smc5/6 Complex Degradation by Mammalian Hepatitis B Virus X Protein","date":"2024-10-28","source":"bioRxiv","url":"https://doi.org/10.1101/2024.10.28.620692","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.07.29.605668","title":"The phenotype of SMC6_G514R hinge mutant of  <i>Physcomitrium patents</i>","date":"2024-07-30","source":"bioRxiv","url":"https://doi.org/10.1101/2024.07.29.605668","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":20481,"output_tokens":6873,"usd":0.082269,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":15744,"output_tokens":5468,"usd":0.10771,"stage2_stop_reason":"end_turn"},"total_usd":0.189979,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"SMC6 forms a high-molecular-mass complex with SMC5 and the non-SMC subunit NSE1 (identified by mass spectrometry after purification of fission yeast Smc5), establishing the core composition of the Smc5-6 complex required for DNA repair and proliferation.\",\n      \"method\": \"Affinity purification and mass spectrometry; co-immunoprecipitation; genetic epistasis with Rhp51\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP, MS identification, genetic epistasis, replicated across organisms\",\n      \"pmids\": [\"12966087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"NSE1 and NSE2 are essential non-SMC subunits of the fission yeast Smc5-6 complex that interact with Smc5 in vivo; loss of Nse1 or Nse2 produces phenotypes identical to Smc5-6 inactivation, and epistasis places them in the same homologous-recombination DSB repair pathway as Rhp51.\",\n      \"method\": \"Affinity purification/mass spectrometry, co-IP, genetic epistasis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — co-IP confirmed subunit membership, epistasis defined pathway, replicated across labs\",\n      \"pmids\": [\"12966087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"NSE3 is an additional essential non-SMC subunit of the fission yeast Smc5-6 complex; it is required for mitotic chromosome segregation, resistance to genotoxic agents, and meiotic recombination-based DNA repair in a pathway epistatic to Rhp51.\",\n      \"method\": \"Biochemical purification, genetic epistasis, co-immunoprecipitation\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — biochemical isolation plus epistasis, replicated in two SMC5/6 subunit studies\",\n      \"pmids\": [\"15331764\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The Smc5/6 complex is required for coordinated DNA damage response: fission yeast cells lacking functional Smc6 initiate a normal Chk1 checkpoint but then enter lethal mitosis, indicating Smc5/6 is needed to maintain checkpoint arrest through ongoing DNA repair rather than for checkpoint initiation.\",\n      \"method\": \"Genetic loss-of-function (smc6 and nse1 mutants), checkpoint kinase phosphorylation assays, live-cell phenotyping\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined cellular phenotype, single lab, two readouts (Chk1 phosphorylation + lethal mitosis)\",\n      \"pmids\": [\"14701739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Rad62 physically associates with the Smc5-6 complex and is required for recombinational repair of DSBs and recovery from stalled replication; its DNA repair role is epistatic with rhp51 and genetically interacts with rad60 and smc6.\",\n      \"method\": \"Co-immunoprecipitation, genetic epistasis, sensitivity assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus epistasis, single lab\",\n      \"pmids\": [\"15485909\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SMC6 is required for MMS-induced sister chromatid recombination and interchromosomal recombination in budding yeast; smc6-56 rad52 double mutants show MMS sensitivity similar to rad52 alone, placing Smc6 in the Rad52-dependent recombination pathway.\",\n      \"method\": \"Temperature-sensitive smc6 mutants, genetic epistasis with rad52, recombination assays\",\n      \"journal\": \"DNA repair\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis with two orthogonal readouts (sensitivity + recombination frequency), single lab\",\n      \"pmids\": [\"15010319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Smc5 and Smc6 are enriched at rDNA and telomeres; conditional smc5-6 and smc6-9 mutants show impaired segregation of repetitive chromosomal regions, accumulation of Holliday junctions at rDNA, and RAD9-dependent Rad53 activation; deletion of RAD52 partially suppresses temperature sensitivity, indicating the complex prevents sister chromatid junctions at repetitive loci.\",\n      \"method\": \"ChIP, 2D gel electrophoresis (Holliday junction detection), genetic epistasis, conditional mutants\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ChIP localization + 2D gel biochemistry + epistasis, multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"15793567\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"NSE1 and NSE2 (with NSE3-NSE4) form a subcomplex within the Smc5-6 holocomplex; NSE4 is identified as the kleisin component that bridges the Smc5 and Smc6 head domains, with its C-terminal region interacting with the Smc5 head and a predicted winged-helix motif required for this interaction.\",\n      \"method\": \"Co-immunoprecipitation, yeast two-hybrid, in vitro binding with purified recombinant proteins, domain mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with mutagenesis, structural prediction validated biochemically, single lab\",\n      \"pmids\": [\"17005570\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Nse5 and Nse6 form a distinct heterodimeric subcomplex within the Smc5-6 holocomplex; Nse5/6 mutants display high spontaneous DNA damage and are required for tolerance of UV lesions and stabilization/processing of stalled replication forks; their UV sensitivity is suppressed by deletion of Rad51 homolog Rhp51, and viability requires Mus81 and Rqh1, implicating Nse5/6 in suppressing aberrant recombination at replication forks.\",\n      \"method\": \"Genetic epistasis, sensitivity assays, RusA rescue experiment\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic epistasis with multiple suppressors, single lab\",\n      \"pmids\": [\"16478984\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The Smc5-Smc6 complex is recruited de novo to DSBs and is essential for repair by homologous recombination between sister chromatids (SCR), and suppresses gross chromosomal rearrangements by preventing non-sister recombination events.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) at induced DSBs, genetic epistasis, GCR assays\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ChIP demonstrating recruitment + GCR assays + genetic epistasis, replicated across studies\",\n      \"pmids\": [\"16892052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Smc5-Smc6 and Mre11 complexes mediate the nucleolar exclusion of Rad52 recombination foci at rDNA DSBs; this exclusion depends on SUMO modification of Rad52. Failure of this pathway leads to Rad52 foci within the nucleolus, rDNA hyperrecombination, and excision of extrachromosomal rDNA circles.\",\n      \"method\": \"Live fluorescence microscopy, SUMO modification assays, genetic epistasis\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct imaging of relocalization + biochemical SUMO modification + genetic rescue, multiple orthogonal methods\",\n      \"pmids\": [\"17643116\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Nse1, a subunit of the Smc5-Smc6 complex, is required for Rad52-dependent post-replication repair (PRR) of UV-damaged DNA; genetic analysis implicates both the Nse1 ubiquitin-ligase-like activity and the Mms21 SUMO-ligase activity of the complex in this Rad52-dependent repair mode.\",\n      \"method\": \"Genetic epistasis, UV sensitivity assays, allele-specific mutant analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis with multiple alleles, single lab\",\n      \"pmids\": [\"17923688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The Nse1 RING-like domain supports Smc5-Smc6 holocomplex integrity: it is required for normal Nse1-Nse3-Nse4 trimer formation in vitro and for damage-induced recruitment of Nse4 and Smc5 to subnuclear foci in vivo. No ubiquitin E3 ligase activity was detected for full-length or isolated Nse1 RING domain in vitro.\",\n      \"method\": \"In vitro ubiquitin ligase assay, co-IP, in vivo focus formation (immunofluorescence), mutagenesis\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro reconstitution (negative result for ligase) + co-IP + live imaging, single lab\",\n      \"pmids\": [\"18667531\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The smc6-9 mutation increases translocation-class gross chromosomal rearrangements (GCRs) in a manner dependent on break-induced replication (BIR) and independent of NHEJ; translocations cluster near repetitive sequences, showing that Smc5-Smc6 suppresses GCR formation by reducing DNA damage at repetitive loci.\",\n      \"method\": \"GCR assay, genetic epistasis (BIR and NHEJ mutants), genome sequencing of rearrangements\",\n      \"journal\": \"DNA repair\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with defined pathway, single lab\",\n      \"pmids\": [\"18585101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The Nse5-Nse6 heterodimer interacts with the hinge regions of both Smc5 and Smc6, while the Nse1-Nse3-Nse4 subcomplex binds to the head and adjacent coiled-coil of Smc5, and Nse2 binds the middle coiled-coil of Smc5; these three entities occupy distinct sites defining the Smc5/6 complex architecture.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding with purified recombinant proteins\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with purified recombinants + two-hybrid, multiple subunit interactions mapped, single lab\",\n      \"pmids\": [\"19141609\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In smc6 mutants after DNA damage, chromosome arm segregation fails due to aberrant persistence of cohesin that is normally removed by the Separase-independent pathway; overexpression of Separase bypasses this defect and restores viability, identifying defective cohesin removal as a major determinant of mitotic lethality in Smc5-Smc6 mutants.\",\n      \"method\": \"Genetic epistasis, cohesin persistence assays, Separase overexpression rescue\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic rescue with Separase + cohesin persistence biochemistry + epistasis with topoisomerase II mutant, multiple orthogonal approaches\",\n      \"pmids\": [\"19528228\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Smc5 binds strongly and specifically to single-stranded DNA (ssDNA) as a monomer independently of Smc6; this binding is regulated by ATP and is observed with ssDNA of ~60 nt or longer, consistent with substrates generated during DNA replication and repair.\",\n      \"method\": \"In vitro DNA-binding assay with purified recombinant Smc5, ATPase mutagenesis, EMSA\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemistry with purified protein + ATPase mutagenesis, single lab\",\n      \"pmids\": [\"21293191\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Smc6 is a strong DNA-binding protein with preference for single-stranded DNA; it binds DNA independently of other Smc5-6 complex components and its activity is modulated by nucleotides; the minimal ssDNA size for tight association is ~60 nucleotides.\",\n      \"method\": \"In vitro DNA-binding assay with purified recombinant Smc6, EMSA\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemistry with purified protein, single lab\",\n      \"pmids\": [\"22086171\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In meiosis, the Smc5-Smc6 complex is required for removing chromosome linkages (including those independent of Spo11-induced recombination) to allow proper chromosome segregation; the complex localizes to specific chromosome regions during meiotic prophase I.\",\n      \"method\": \"Immunofluorescence localization, genetic (spo11 epistasis), chromosome segregation assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization + epistasis, single lab\",\n      \"pmids\": [\"21731634\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Smc6 mutation leads to accumulation of recombination intermediates at centromeres (assayed by 2D gel) and increased centromere-associated Rad52 foci; a rad52 mutation suppressing centromeric Rad52 foci also suppresses nocodazole sensitivity of smc6 mutants, showing that Smc5-Smc6 regulates recombination at centromeric loci. The SUMO ligase subunit of Smc5-Smc6 (Mms21) also promotes sumoylation of kinetochore proteins and affects mitotic spindles.\",\n      \"method\": \"2D gel electrophoresis, fluorescence microscopy (Rad52 foci co-localization), SUMO modification assays, genetic epistasis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — 2D gel + imaging + biochemical SUMO assay, single lab\",\n      \"pmids\": [\"23284708\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Nse5-Nse6 of the Smc5-Smc6 complex is required for meiotic resolution of Holliday junction-like recombination intermediates (DNA joint molecules) via promotion of Mus81-Eme1 endonuclease activity; RusA bacterial resolvase partially rescues nse6Δ meiotic defects, and elimination of Rec12 (Spo11) nearly completely rescues defects, placing Nse5-Nse6 after DSB formation in the meiotic recombination pathway.\",\n      \"method\": \"Southern blotting for DNA joint molecules, RusA rescue, genetic epistasis (rec12Δ, mus81Δ)\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — biochemical joint molecule detection + genetic rescue + epistasis, multiple orthogonal methods\",\n      \"pmids\": [\"22855558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SMC6 is an essential gene in mice (complete knockout causes early embryonic lethality); a hypomorphic ATPase domain mutation (S994A) results in viable mice with sensitivity to induction of sister chromatid exchanges by UV and mitomycin C, and accumulation of oxidative damage, but not sensitivity to killing by DNA-damaging agents.\",\n      \"method\": \"Gene knockout, ATPase point mutant knockin, sister chromatid exchange assay, embryonic fibroblast sensitivity assays\",\n      \"journal\": \"DNA repair\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout lethality + ATPase mutagenesis in mammals + multiple cellular assays, replicated internally\",\n      \"pmids\": [\"23518413\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"During mouse spermatogenesis, Smc6 localizes to pericentromeric heterochromatin domains specifically when differentiating spermatogonia commit irreversibly toward meiosis; Smc6-negative meiotic cells fail to complete the first meiotic division; DNA repair/recombination sites (γH2AX, Rad51) do not co-localize with the Smc6-positive pericentromeric domains.\",\n      \"method\": \"Immunofluorescence/localization in testis sections, co-localization analysis, meiotic staging\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization in mammalian tissue with meiotic phenotype, single lab\",\n      \"pmids\": [\"23907463\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In Drosophila, SMC6 (CG5524) mutants are hypersensitive to genotoxic agents (ionizing radiation, camptothecin, hydroxyurea, MMS); MAGE physically interacts with Drosophila Nse homologs, indicating conservation of the SMC5/6 complex structure; caffeine-induced apoptosis in smc6 mutants is suppressed by Rad51 depletion, placing SMC6 in a homologous recombination repair pathway.\",\n      \"method\": \"Genetic screen, genotoxin sensitivity assays, co-immunoprecipitation, genetic epistasis (Rad51 depletion)\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP + genetic epistasis, replicated in model organism\",\n      \"pmids\": [\"23555814\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The Smc5-Smc6 heterodimer contains two independent DNA-binding domains (DBDs) in each SMC subunit: one in the hinge/coiled-coil region and one in the ATPase head domain; heterodimerization of full-length proteins specifically increases affinity for double-stranded DNA substrates compared to monomers.\",\n      \"method\": \"In vitro DNA-binding assays with purified recombinant domain fragments, EMSA\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro domain mapping with recombinant proteins, single lab\",\n      \"pmids\": [\"25984708\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Brc1 (fission yeast) is required for the focal accumulation (foci formation) of the Smc5-Smc6 complex during replication stress and for activation of its intrinsic SUMO ligase activity at collapsed replication forks; the Nse5-Nse6 heterodimer is required for chromatin association and SUMO ligase activity of Smc5-Smc6; Brc1 interacts physically with Nse5-Nse6 and with γ-H2A, thereby tethering Smc5-Smc6 at replicative DNA lesions.\",\n      \"method\": \"Co-immunoprecipitation, SUMO ligase activity assay, immunofluorescence focus formation, genetic epistasis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — co-IP + enzymatic assay + imaging, multiple orthogonal methods in single study\",\n      \"pmids\": [\"30348841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"The human SMC5/6 complex is recruited to transcription-replication conflicts (TRCs) in response to DNA supercoiling buildup in SETX-deficient cells; once recruited, SMC5/6 facilitates recruitment of the BLM/TOP3A/RMI1/RMI2 (BTRR) complex, which resolves TRCs in a TOP3A catalytic-activity-dependent manner; BTRR in turn recruits FANCM to activate the FANCD2 pathway, defining the SMC5/6-BTRR-FANCM-FANCD2 axis.\",\n      \"method\": \"Synthetic lethality screen, ChIP/proximity ligation for recruitment, epistasis with TOP3A catalytic mutant, co-immunoprecipitation\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — synthetic lethality + co-IP + catalytic mutant epistasis, multiple orthogonal methods in single study on human cells\",\n      \"pmids\": [\"41533569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cryo-EM structure of the human HBx-CRL4-SMC5/6 complex at 3.1 Å resolution reveals that HBx adopts a zinc-stabilized Y-shaped architecture and directly contacts the SMC6 subunit via a conserved 'Leucine Key' motif (LRCKL) on SMC6 that fits into a helix-turn-helix (HTH) pocket on HBx; disrupting this interface with Tranilast suppresses HBV replication.\",\n      \"method\": \"Cryo-electron microscopy (3.1 Å), reconstitution of ten-subunit complex, molecular docking, biochemical validation, HBV replication assay\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — cryo-EM structure + reconstitution + biochemical validation + functional assay, single preprint study\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SMC5/6-mediated repression of extrachromosomal circular/plasmid DNA transcription depends exclusively on the SIMC1-SLF2 subcomplex (the human counterpart of yeast Nse5/6) and requires a conserved SIMC1-SLF2–SMC6 interaction; SLF1/2 is dispensable for plasmid silencing; plasmid silencing requires the SUMO pathway but not PML nuclear bodies.\",\n      \"method\": \"Reporter-based transcriptional silencing assay, co-immunoprecipitation, genetic knockdown/knockout\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP + functional transcriptional assay, single preprint lab\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"SMC6 is a core ATPase subunit of the conserved SMC5/6 complex that binds single-stranded and double-stranded DNA through hinge and head-domain DBDs, is recruited de novo to DSBs, stalled replication forks, and transcription-replication conflicts, where it promotes sister-chromatid recombination, prevents accumulation of aberrant Holliday junctions at repetitive loci, and facilitates Separase-independent cohesin removal to ensure chromosome segregation; the complex achieves these functions through its associated SUMO ligase (Mms21/NSE2), its Nse5/6 (or human SIMC1-SLF2) regulatory subcomplex that controls chromatin loading and SUMO ligase activation, and an SMC5/6-BTRR-FANCM-FANCD2 axis that resolves transcription-replication conflicts, while the SMC6 subunit itself is directly targeted for degradation by viral proteins (HBx) that bind the SMC6 'Leucine Key' motif to counteract restriction of viral episomes.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SMC6 is a core ATPase subunit of the conserved SMC5/6 complex that governs the recombinational repair and segregation of damaged and repetitive chromosomes [#0, #9]. Together with SMC5 it forms the structural heterodimer of a holocomplex that incorporates the essential non-SMC subunits NSE1, NSE2, NSE3, and the NSE4 kleisin bridging the two SMC head domains, plus the NSE5/NSE6 heterodimer that contacts the SMC hinges [#0, #1, #2, #7, #14]. SMC6 itself is a strong, nucleotide-modulated DNA-binding protein with two independent DNA-binding domains — one in the hinge/coiled-coil region and one in the ATPase head — that prefer single-stranded DNA as monomers but gain double-stranded DNA affinity upon heterodimerization with SMC5 [#16, #17, #24]. The complex is recruited de novo to double-strand breaks and is essential for homologous recombination between sister chromatids while suppressing non-sister recombination and gross chromosomal rearrangements, particularly at repetitive loci such as rDNA, telomeres, and centromeres where it prevents accumulation of aberrant Holliday-junction intermediates [#6, #9, #13, #19]. At collapsed replication forks SMC5/6 is tethered through an NSE5/6–Brc1–γ-H2A interaction that licenses its chromatin association and intrinsic SUMO ligase activity [#25], and in human cells it is recruited to transcription–replication conflicts where it nucleates a BTRR–FANCM–FANCD2 resolution axis [#26]. SMC6 function ensures faithful chromosome segregation by enabling Separase-independent cohesin removal after DNA damage [#15] and is required during meiosis to remove chromosome linkages [#18, #20]. SMC6 is essential in mice, with ATPase-domain integrity required to limit damage-induced sister chromatid exchange and oxidative damage [#21]. The SMC6 subunit is directly targeted by the hepatitis B virus protein HBx, which engages a conserved 'Leucine Key' (LRCKL) motif on SMC6 to neutralize its restriction of viral episomal DNA [#27, #28].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established the core subunit composition of the SMC5/6 complex, defining SMC6 as part of a multi-subunit machine rather than a standalone factor and placing it in a Rhp51-dependent DNA repair pathway.\",\n      \"evidence\": \"Affinity purification/mass spectrometry, co-IP, and genetic epistasis in fission yeast\",\n      \"pmids\": [\"12966087\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and architecture of subunit contacts not yet resolved\", \"Biochemical activity of the complex undefined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identified NSE3 as an additional essential non-SMC subunit and showed SMC5/6 is required to sustain checkpoint-coupled repair — cells initiate Chk1 but enter lethal mitosis — distinguishing a repair/maintenance role from checkpoint initiation.\",\n      \"evidence\": \"Biochemical purification, checkpoint kinase phosphorylation assays, and live-cell phenotyping in fission yeast\",\n      \"pmids\": [\"15331764\", \"14701739\", \"15485909\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism by which the complex maintains arrest not defined\", \"Direct DNA substrate not identified\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Placed SMC6 directly in the Rad52/Rad51-dependent recombination pathway by showing it is required for MMS-induced sister chromatid and interchromosomal recombination.\",\n      \"evidence\": \"Temperature-sensitive smc6 mutants with epistasis to rad52 and recombination assays in budding yeast\",\n      \"pmids\": [\"15010319\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether SMC5/6 acts before or after strand invasion unresolved\", \"No biochemical reconstitution of its recombination role\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Localized SMC5/6 to rDNA and telomeres and demonstrated it prevents accumulation of Holliday junctions at repetitive loci, explaining its role in segregating repetitive chromosomal regions.\",\n      \"evidence\": \"ChIP, 2D-gel Holliday junction detection, and genetic epistasis in conditional mutants\",\n      \"pmids\": [\"15793567\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which junctions are prevented vs resolved not separated\", \"Direct enzymatic activity on junctions not shown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Resolved the internal architecture of the complex, identifying NSE4 as the kleisin bridging SMC5 and SMC6 heads, and defining NSE5/6 as a distinct hinge-associated subcomplex required for replication fork stability.\",\n      \"evidence\": \"In vitro binding with recombinant proteins, yeast two-hybrid, domain mutagenesis, and genetic epistasis\",\n      \"pmids\": [\"17005570\", \"16478984\", \"16892052\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How head-bridging kleisin couples to ATPase cycle unknown\", \"Functional consequence of hinge-head geometry on DNA handling unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Linked SMC5/6 to SUMO-dependent spatial control of recombination by showing it excludes Rad52 foci from the nucleolus to prevent rDNA hyperrecombination, and connected NSE1 and the Mms21 SUMO ligase to Rad52-dependent post-replication repair.\",\n      \"evidence\": \"Live fluorescence microscopy, SUMO modification assays, and allele-specific genetic analysis\",\n      \"pmids\": [\"17643116\", \"17923688\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"SUMO substrates driving exclusion not fully enumerated\", \"Mechanism connecting NSE1 RING to repair undefined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Clarified that the NSE1 RING-like domain supports holocomplex integrity and damage-induced focus recruitment rather than acting as a detectable ubiquitin ligase, refining the functional assignment of complex subunits.\",\n      \"evidence\": \"In vitro ubiquitin ligase assays (negative), co-IP, in vivo focus formation, and mutagenesis; plus GCR assays showing BIR-dependent translocation suppression\",\n      \"pmids\": [\"18667531\", \"18585101\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether NSE1 has E3 activity in a different context unresolved\", \"Substrate of any associated ligase not identified here\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Mapped the spatial organization of all subcomplexes onto SMC5/6 (NSE5/6 at hinges, NSE1-3-4 at SMC5 head, NSE2 at middle coiled-coil) and revealed that mitotic lethality of smc6 mutants arises from failed Separase-independent cohesin removal.\",\n      \"evidence\": \"Yeast two-hybrid and in vitro binding for architecture; Separase overexpression rescue and cohesin persistence assays for segregation\",\n      \"pmids\": [\"19141609\", \"19528228\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism linking SMC5/6 to cohesin removal undefined\", \"How architecture supports cohesin function not established\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defined the biochemical DNA-binding behaviour of SMC6 and SMC5, showing each is a strong, nucleotide-modulated, ssDNA-preferring binder as a monomer, consistent with engaging replication/repair intermediates.\",\n      \"evidence\": \"In vitro EMSA DNA-binding assays with purified recombinant SMC5 and SMC6 and ATPase mutagenesis\",\n      \"pmids\": [\"21293191\", \"22086171\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological DNA substrate not confirmed in vivo\", \"Coupling of binding to ATPase cycle not resolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Extended SMC5/6 function into meiosis, showing it removes chromosome linkages including Spo11-independent ones to permit segregation, and localizes to specific prophase chromosome regions.\",\n      \"evidence\": \"Immunofluorescence localization, spo11 epistasis, and chromosome segregation assays\",\n      \"pmids\": [\"21731634\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Nature of the removed linkages unclear\", \"Mechanism of region-specific localization unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed SMC5/6 regulates recombination at centromeres and that its Mms21 SUMO ligase sumoylates kinetochore proteins, and established that NSE5/6 promotes meiotic resolution of joint molecules via Mus81-Eme1.\",\n      \"evidence\": \"2D gels for recombination intermediates, Rad52 foci imaging, SUMO assays, Southern blotting for joint molecules, RusA rescue, and epistasis\",\n      \"pmids\": [\"23284708\", \"22855558\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct kinetochore SUMO targets not fully validated\", \"How NSE5/6 stimulates Mus81-Eme1 mechanistically unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Established SMC6 as essential in a mammal and tied ATPase integrity to suppression of sister chromatid exchange and oxidative damage, while documenting conservation of complex structure and HR function across Drosophila and mouse spermatogenesis.\",\n      \"evidence\": \"Mouse knockout, ATPase S994A knockin, sister chromatid exchange assays, immunofluorescence in testis, Drosophila genotoxin sensitivity and co-IP\",\n      \"pmids\": [\"23518413\", \"23907463\", \"23555814\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Embryonic-lethal step in knockout not defined\", \"Role of pericentromeric SMC6 localization in meiotic commitment unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Resolved the DNA-binding module organization, demonstrating two independent DBDs per SMC subunit (hinge/coiled-coil and ATPase head) and that heterodimerization increases dsDNA affinity, providing a structural basis for substrate engagement.\",\n      \"evidence\": \"In vitro EMSA with purified recombinant domain fragments\",\n      \"pmids\": [\"25984708\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo contribution of each DBD not dissected\", \"How DNA binding is coordinated with ATP hydrolysis unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined the recruitment logic at collapsed replication forks: Brc1 bridges NSE5/6 and γ-H2A to tether SMC5/6 and activate its intrinsic SUMO ligase, explaining how the complex is targeted to replicative lesions.\",\n      \"evidence\": \"Co-IP, SUMO ligase activity assays, focus-formation imaging, and genetic epistasis in fission yeast\",\n      \"pmids\": [\"30348841\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Human counterpart of this tether not addressed here\", \"SUMO ligase substrates at forks not enumerated\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Placed human SMC5/6 at the head of a transcription-replication conflict resolution axis, showing it recruits the BTRR complex (resolving via TOP3A catalysis) which then recruits FANCM to activate FANCD2.\",\n      \"evidence\": \"Synthetic lethality screen, ChIP/proximity ligation, TOP3A catalytic-mutant epistasis, and co-IP in human cells\",\n      \"pmids\": [\"41533569\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How SMC5/6 senses supercoiling buildup not defined\", \"Direct SMC6–BTRR contacts not mapped structurally\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined the human regulatory subcomplex and viral antagonism interface: SIMC1-SLF2 (the Nse5/6 counterpart) is required for SMC5/6-mediated silencing of extrachromosomal DNA, and HBx engages a conserved SMC6 'Leucine Key' motif to counteract this restriction.\",\n      \"evidence\": \"Cryo-EM of the HBx-CRL4-SMC5/6 complex (preprint), reconstitution, reporter silencing assays, co-IP, and HBV replication assays\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Both reports are single-lab preprints awaiting peer review\", \"Mechanism by which SIMC1-SLF2–SMC6 contact drives transcriptional silencing not defined\", \"How SUMO pathway dependence connects to silencing unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the SMC6 ATPase cycle, its two DNA-binding domains, and SUMO ligase activation are mechanically coupled to discriminate and resolve recombination intermediates at distinct genomic loci remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No integrated structure-function model linking ATP hydrolysis to DNA loop/junction handling\", \"Direct enzymatic activity of the complex on Holliday junctions not demonstrated\", \"Full SUMO substrate landscape across loci undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [16, 21]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [16, 17, 24]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 7, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [9, 12, 25]},\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [6, 10]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [6, 19, 22]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [9, 5, 6]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [15, 18]},\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [8, 25, 26]}\n    ],\n    \"complexes\": [\n      \"SMC5/6 complex\",\n      \"NSE1-NSE3-NSE4 subcomplex\",\n      \"NSE5/NSE6 (SIMC1-SLF2) subcomplex\"\n    ],\n    \"partners\": [\n      \"SMC5\",\n      \"NSE1\",\n      \"NSE2\",\n      \"NSE3\",\n      \"NSE4\",\n      \"NSE5\",\n      \"NSE6\",\n      \"HBx\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":7,"faith_total":7,"faith_pct":100.0}}