{"gene":"SUPT16H","run_date":"2026-06-10T10:51:54","timeline":{"discoveries":[{"year":1999,"finding":"FACT complex comprises human SPT16 (SUPT16H, homologue of yeast Spt16/Cdc68) and SSRP1 proteins; FACT specifically interacts with nucleosomes and histone H2A/H2B dimers and functions as a chromatin-specific transcription elongation factor required for transcription of chromatin templates in vitro; FACT activity is abrogated by covalent crosslinking of nucleosomal histones, indicating it works by promoting nucleosome disassembly.","method":"Biochemical purification, reconstituted in vitro transcription on chromatin templates, direct binding assays (nucleosome and H2A/H2B interaction), crosslinking experiments","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro chromatin transcription assay, direct binding to nucleosomes/H2A-H2B demonstrated, functional abrogation by crosslinking; foundational paper replicated by many subsequent studies","pmids":["10421373"],"is_preprint":false},{"year":1991,"finding":"SPT16/CDC68 (yeast orthologue of SUPT16H) is an essential gene in S. cerevisiae required for normal transcription at multiple loci; temperature-sensitive spt16 alleles suppress delta insertion mutations and upstream activating sequence deletions, demonstrating a role in promoter function; SPT16 is identical to CDC68, previously shown to be required for passage through cell-cycle START, but transcriptional effects of spt16 mutations are at least partially independent of cell-cycle arrest.","method":"Null mutation construction, temperature-sensitive allele isolation, genetic suppression assays, epistasis analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic epistasis experiments in yeast, null and conditional alleles, replicated by accompanying paper; foundational genetic characterization","pmids":["1922073"],"is_preprint":false},{"year":2008,"finding":"The N-terminal 'peptidase homology' domain of fission yeast Spt16 (Spt16-N) is a histone H3-H4 binding module; crystal structure at 2.1 Å reveals an aminopeptidase P fold that has lost enzymatic activity but directly binds the globular core domains and N-terminal tails of H3-H4; mutations in a conserved surface pocket in Spt16-N or posttranslational modification of the H4 tail reduce interaction in vitro.","method":"X-ray crystallography (2.1 Å), biochemical binding assays, site-directed mutagenesis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus mutagenesis and in vitro binding assays in a single rigorous study; single lab but multiple orthogonal methods","pmids":["18579787"],"is_preprint":false},{"year":2019,"finding":"Cryo-EM structures of human FACT (SPT16/SSRP1) in complex with partially assembled subnucleosomes reveal: (1) FACT engages extensively with nucleosomal DNA and all histone variants; (2) the C-terminal domains (CTDs) of both SPT16 and SSRP1 protect the DNA-binding surface; (3) interaction with H2A-H2B releases this inhibition allowing FACT-H2A-H2B to dock onto a DNA/H3-H4 complex; (4) SPT16 CTD acts as a placeholder for DNA by tethering H2A-H2B; (5) SSRP1 can adopt two conformations depending on whether a second H2A-H2B dimer is present. This mechanism facilitates H2A-H2B dimer removal, stabilizes subnucleosomal intermediates, and promotes reassembly.","method":"Cryo-electron microscopy (two structures), hydrogen-deuterium exchange mass spectrometry, biochemical binding assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — two independent cryo-EM structures with supporting HDX-MS and biochemical data; multiple orthogonal methods in one rigorous study","pmids":["31775157"],"is_preprint":false},{"year":2018,"finding":"SPT16 (large subunit of FACT) destabilizes the nucleosome by displacing H2A/H2B dimers at the single-nucleosome level, while SSRP1 (small subunit) maintains nucleosome integrity by holding the H3/H4 tetramer on DNA and promoting deposition of H2A/H2B dimers; the two subunits thus play opposing but coordinated roles in nucleosome remodeling.","method":"Single-nucleosome FRET, biochemical reconstitution, subunit-specific functional dissection","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — single-molecule FRET reconstitution with biochemical dissection of individual subunit functions; single lab, multiple orthogonal approaches","pmids":["30029006"],"is_preprint":false},{"year":2021,"finding":"Cryo-EM structures of transcribing yeast RNA Pol II-Spt4/5-nucleosome complexes show that FACT binds a partially unraveled nucleosome generated during Pol II transcription, excludes Chd1 and Spt5, and is positioned to facilitate nucleosome reassembly upstream; biochemically, FACT facilitates Pol II transcription through a nucleosome when Spt4/5 and TFIIS are present.","method":"Cryo-electron microscopy, in vitro transcription reconstitution on chromatin templates","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structures plus in vitro reconstituted transcription assay; multiple orthogonal methods","pmids":["33846633"],"is_preprint":false},{"year":2009,"finding":"FACT (SSRP1 and SPT16 subunits) co-purifies and co-immunoprecipitates with mammalian RNA Pol I complexes; SSRP1 is detectable at rRNA gene repeats by ChIP; siRNA knockdown of FACT subunits reduces 47S pre-rRNA levels without affecting synthesis of the first 40 nt of rRNA, placing FACT function specifically at Pol I elongation through chromatin. FACT also associates with Pol III complexes and facilitates Pol III-transcribed gene expression.","method":"Co-immunoprecipitation, chromatin immunoprecipitation (ChIP), siRNA knockdown, run-on transcription assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP, ChIP localization, and functional siRNA knockdown with specific elongation phenotype; multiple orthogonal methods in one study","pmids":["19214185"],"is_preprint":false},{"year":2005,"finding":"Yeast FACT (yFACT) promotes TBP binding to a TATA box within a reconstituted nucleosome in a TFIIA-dependent manner in vitro; in vivo, certain spt16 mutations are synthetically lethal with TBP and TFIIA (TOA2) mutants, and spt16 mutations reduce TBP binding to promoters by ChIP, establishing a role for SPT16 in transcription initiation as well as elongation.","method":"In vitro TBP-nucleosome binding reconstitution, genetic synthetic lethality, chromatin immunoprecipitation (ChIP)","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro reconstitution plus genetic epistasis plus ChIP; multiple orthogonal methods in one study","pmids":["15987999"],"is_preprint":false},{"year":2009,"finding":"At the yeast HO promoter, FACT (SPT16-containing complex) is required for nucleosome eviction at distinct promoter regions; FACT and Asf1 bind upstream HO promoter elements before transcription initiation and are both required for re-recruitment of Swi/Snf, SAGA, and Mediator coactivators to promoter-proximal regions.","method":"Chromatin immunoprecipitation (ChIP), genetic epistasis with chromatin modifier mutants, cell-cycle-resolved ChIP analysis","journal":"Molecular cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP-based dissection of nucleosome dynamics and coactivator recruitment at a specific promoter; single lab, multiple gene deletions and ChIP analyses","pmids":["19481521"],"is_preprint":false},{"year":2016,"finding":"FACT (Spt16-Pob3 in yeast) promotes newly synthesized histone H3-H4 deposition during DNA replication-coupled nucleosome assembly; an spt16 allele (spt16-m) defective in H3-H4 binding impairs their deposition; FACT physically associates with Rtt106 and the H3K56 acetylation mark on newly synthesized H3 modulates this interaction; FACT shows synthetic defects with CAF-1 and Rtt106.","method":"Genetic epistasis (synthetic lethality), in vitro H3-H4 binding assays, co-immunoprecipitation, site-directed mutagenesis, histone deposition assay","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — reconstituted binding assays with mutant allele, co-IP with Rtt106, genetic epistasis; multiple orthogonal approaches in one study","pmids":["26804921"],"is_preprint":false},{"year":2011,"finding":"SUPT16H (SPT16, a FACT subunit) is required for RNF20-mediated H2B ubiquitylation at sites of DNA double-strand breaks; depletion of SUPT16H causes defective accumulation of repair proteins (RAD51, BRCA1), decreased H3K56ac, sustained γH2AX phosphorylation, impaired DNA end resection, delayed DSB repair, and decreased recruitment of SNF2h; SUPT16H directly binds RNF20 in vivo; PAF1 is dispensable for DNA damage-induced SUPT16H-RNF20 interaction.","method":"siRNA knockdown, co-immunoprecipitation, γH2AX foci imaging, H3K56ac quantification, homologous recombination reporter assay, ionizing radiation sensitivity","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple siRNA knockdowns phenocopying each other, co-IP, and functional repair assays; single lab, multiple readouts","pmids":["22031019"],"is_preprint":false},{"year":2013,"finding":"SUPT16H (FACT) is required for RNF20 recruitment to DNA double-strand break sites and subsequent H2B ubiquitylation; SUPT16H directly binds RNF20 in vivo and is required for SNF2h accumulation and chromatin relaxation at DSBs; SUPT16H depletion causes radiation and mitomycin-C sensitivity and decreased homologous recombination activity; enforced nucleosome relaxation counteracts SUPT16H-deficient phenotypes.","method":"siRNA knockdown, co-immunoprecipitation, immunofluorescence foci assays, HR reporter assay, clonogenic survival assay","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus functional HR and repair assays; single lab, multiple orthogonal readouts","pmids":["24357716"],"is_preprint":false},{"year":2003,"finding":"FACT (Spt16 subunit) forms a stable ~600 kDa complex with the kinase Nek9 in interphase nuclei; when complexed with FACT, Nek9 exhibits elevated phosphorylation on Thr210 (activation loop); Nek9 RNAi causes defects in G1 and S phase progression, phenotypically linked to the phospho-Nek9-FACT complex formation.","method":"Co-immunoprecipitation, size-exclusion chromatography, phosphorylation analysis, RNA interference cell-cycle analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — stable complex identified by co-IP and gel filtration, phosphorylation state characterized, RNAi phenotype; single lab, single co-IP with supporting functional data","pmids":["14660563"],"is_preprint":false},{"year":2004,"finding":"Domain organization of yeast FACT: FACT integrity depends on Pob3 interactions with the Spt16 Mid domain; the conserved Spt16 N-terminal domain (NTD) is dispensable for normal growth but becomes important under replication stress conditions; genetic interactions suggest some Spt16 NTD functions are partially redundant within FACT.","method":"Genetic analysis (deletion alleles, synthetic lethality), biochemical fractionation","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic domain dissection with multiple alleles and biochemical fractionation; single lab","pmids":["15520471"],"is_preprint":false},{"year":2017,"finding":"FACT (via its SSRP1 subunit/CID domain) binds Z-DNA or DNA in transition from B to Z form in cells treated with curaxin; purified SSRP1 CID domain binds methylated alternating purine/pyrimidine DNA (prone to Z-DNA transition) more strongly than other DNA types in vitro; FACT binding to these alternative DNA structure regions triggers a p53 response, positioning FACT as a sensor of DNA torsional stress.","method":"ChIP after curaxin treatment, in vitro DNA binding assays with purified SSRP1/CID, p53 response assay","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro binding assay plus in-cell ChIP localization plus functional p53 readout; single lab, multiple orthogonal methods","pmids":["28082391"],"is_preprint":false},{"year":2015,"finding":"SUPT16H (SPT16) interacts with HIV-1 Tat protein (but not SSRP1); both SUPT16H and SSRP1 are recruited to the HIV-1 LTR promoter; SUPT16H presence interferes with Cyclin T1 (P-TEFb subunit) association with the Tat-LTR axis; depletion of SUPT16H or SSRP1 enhances Tat-mediated LTR activity, affects transcriptional initiation and elongation, and spontaneously reverses HIV-1 latency in cell models.","method":"Co-immunoprecipitation, ChIP, RNAi knockdown, HIV-1 latency reactivation assay, LTR reporter assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP, ChIP, and functional knockdown with latency phenotype; single lab, multiple orthogonal methods","pmids":["26378236"],"is_preprint":false},{"year":2019,"finding":"FACT stimulates Ubp10 deubiquitinase activity specifically on nucleosome substrates (not other substrates); a FACT mutant strain shows elevated H2B monoubiquitination in vivo; combination of FACT mutants with deletion of Ubp10 (but not Ubp8) confers increased sensitivity to hydroxyurea and activates cryptic transcription, indicating FACT and Ubp10 coordinate nucleosome assembly during DNA replication and transcription.","method":"In vitro deubiquitination assay with reconstituted nucleosomes, H2B-Ub immunoblotting in FACT mutant strains, genetic epistasis (double mutants), cryptic transcription reporter assay","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstituted deubiquitination assay plus in vivo H2B-Ub measurement plus genetic epistasis; multiple orthogonal methods in one study","pmids":["30681413"],"is_preprint":false},{"year":2019,"finding":"FACT globally represses antisense transcripts near the 5' end of genes in S. pombe; H2B ubiquitination (H2Bub) is required for FACT activity in genic regions—in the H2Bub mutant, FACT binding to chromatin is altered and its association with histones stabilized, leading to reduction of genic nucleosomes; FACT depletion globally restores nucleosomes lost in the H2Bub mutant; FACT (specifically Spt16 subunit absent Pob3) also controls the 3' end processing of genes and maintains nucleosomes in subtelomeric regions required for their compaction.","method":"RNA-seq, ChIP-seq, genome-wide nucleosome mapping, genetic (H2Bub mutant and FACT depletion), co-immunoprecipitation, microscopy","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genomics, genetic epistasis, biochemistry, and microscopy across multiple orthogonal approaches; replicated across conditions","pmids":["31837996"],"is_preprint":false},{"year":2019,"finding":"FACT mediates cohesin function on chromatin: FACT interacts directly with cohesin, is dynamically required for cohesin localization on chromatin; depletion of FACT in metaphase cells prevents cohesin accumulation at pericentric regions and reduces binding on chromosome arms; FACT depletion reduces cohesin-dependent TAD-like structures in both G1 and metaphase chromosomes by Hi-C, although sister chromatid cohesion itself is intact.","method":"Co-immunoprecipitation (FACT-cohesin), ChIP-seq (cohesin localization), Hi-C (TAD analysis), conditional FACT depletion","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct co-IP between FACT and cohesin, ChIP-seq, Hi-C, conditional depletion; multiple orthogonal methods in one study","pmids":["31582854"],"is_preprint":false},{"year":2019,"finding":"OTUD5 deubiquitinase interacts with FACT component SPT16 and antagonizes H2A deposition at DNA double-strand break lesions; OTUD5-SPT16 interaction (along with OTUD5-UBR5 interaction) is required for arresting RNA Pol II elongation at DSB lesions; a cancer-associated missense mutation in OTUD5 UIM abrogates FACT association and Pol II arrest.","method":"DUB RNAi screen, co-immunoprecipitation, immunofluorescence, RNA synthesis assay at DSBs","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP, RNAi screen validation, and functional Pol II arrest assay; single lab, multiple readouts","pmids":["30508113"],"is_preprint":false},{"year":2019,"finding":"FACT and Spt6 are required for local recycling of modified histones during transcription in S. cerevisiae; disruption of FACT or Spt6 causes nucleosome loss that is partially compensated by non-transcription-coupled chaperones; in the absence of functional FACT or Spt6, transcription-evicted modified histones are randomly incorporated, scrambling epigenomic information.","method":"ChIP-seq for histone modifications in FACT/Spt6 mutant strains, nucleosome mapping, genetic analysis","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genome-wide ChIP-seq in defined mutants with mechanistic interpretation; single lab","pmids":["31365865"],"is_preprint":false},{"year":2018,"finding":"FACT acts as a barrier to cell fate reprogramming in C. elegans and humans: FACT depletion in C. elegans identified in a genetic screen as maintaining cell identity; FACT depletion enhances reprogramming of human fibroblasts to iPSCs; a subset of FACT-occupied genes (including reprogramming-promoting factors) shows increased expression upon FACT depletion, revealing a repressive function of FACT at specific loci.","method":"Genetic screen (C. elegans), siRNA/shRNA knockdown, iPSC reprogramming efficiency assay, RNA-seq, ChIP-seq","journal":"Developmental cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic screen plus mammalian knockdown with reprogramming phenotype and RNA-seq; cross-species conservation; single lab","pmids":["30078731"],"is_preprint":false},{"year":2020,"finding":"FACT is essential to overcome replication stress in mammalian cells: in the absence of FACT during replication stress, the MCM2-7 helicase dissociates from chromatin, resulting in absence of ssDNA accumulation, RPA binding, and ATR/CHK1 checkpoint activation; without this response, stalled replication forks are not stabilized, new origin firing is not prevented, and DNA damage and cell death accumulate.","method":"Genetic knockdown/knockout, chromatin fractionation (MCM2-7 dissociation), RPA immunofluorescence, ATR/CHK1 phosphorylation analysis, DNA fiber assay, hydroxyurea/APH treatment","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal assays (chromatin fractionation, checkpoint signaling, DNA fiber) with specific molecular mechanism; single lab","pmids":["32533099"],"is_preprint":false},{"year":2022,"finding":"FACT (SSRP1 and SUPT16H) interacts with transcription factors TFEB and TFE3 in the nucleus upon nutrient deprivation or oxidative stress; FACT depletion (siRNA or curaxin inhibitor) does not affect TFEB activation, stability, or promoter binding, but severely impairs induction of antioxidant and lysosomal target genes; FACT is required downstream of TFEB/TFE3 binding for chromatin remodeling at stress-responsive gene promoters.","method":"Co-immunoprecipitation, siRNA knockdown, curaxin inhibitor treatment, RT-qPCR, ChIP","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP, knockdown and inhibitor with gene expression readouts, ChIP; single lab, multiple approaches","pmids":["35230915"],"is_preprint":false},{"year":2022,"finding":"Recruitment of FACT to the replication fork requires the N-terminal domain of Spt16, which directly interacts with the fork protection complex subunit Tof1; single-molecule FRET demonstrates that nucleosomal DNA reorganization by FACT requires coordinated engagement by the middle and C-terminal domains of Spt16 and Pob3 (but not Spt16 N-terminus); this Tof1-Spt16 NTD interaction is required for robust in vitro chromatin replication.","method":"Single-molecule FRET, structure-guided pulldowns, in vitro chromatin replication assay","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — single-molecule FRET reconstitution, pulldown binding assay, in vitro replication assay; multiple orthogonal methods in one study","pmids":["35061899"],"is_preprint":false},{"year":2022,"finding":"Pyruvate produced by PKM2 directly binds SSRP1 subunit of the FACT complex, increasing FACT association with γH2AX and facilitating FACT-mediated chromatin loading of γH2AX to promote DNA repair; PKM2 is phosphorylated at S222 upon DNA damage and interacts with the FACT complex (SPT16 and SSRP1); exogenous pyruvate supplementation is sufficient to enhance FACT-mediated γH2AX chromatin loading.","method":"Co-immunoprecipitation, in vitro binding assay (pyruvate-SSRP1), γH2AX chromatin loading assay, PKM2 phospho-mutant analysis, clonogenic survival","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP, in vitro binding, functional γH2AX loading assay; single lab, multiple orthogonal methods","pmids":["35048565"],"is_preprint":false},{"year":2024,"finding":"Rapid depletion of FACT from human cells in vivo destabilizes chromatin and leads to: (1) defective promoter-proximal RNA Pol II pausing dependent on the +1 nucleosome maintained by FACT; (2) elongation defects; (3) increased premature termination of Pol II; demonstrating that FACT maintains chromatin architecture in vivo to support pausing and productive elongation.","method":"Rapid auxin-inducible degron (AID) FACT depletion, multi-omics (ChIP-seq, PRO-seq, RNA-seq, ATAC-seq/MNase-seq)","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — rapid in vivo depletion with multi-omics readouts identifying specific mechanistic defects; multiple orthogonal genome-wide methods","pmids":["38810649"],"is_preprint":false},{"year":2020,"finding":"FACT (SSRP1 subunit) recruits H2B deubiquitinase Usp7 to SSRP1 target genes in mouse ESCs; Ssrp1 interacts with MERVL retrotransposon sequences and suppresses cryptic MERVL-derived transcription; loss of Ssrp1 activates MERVL ERVs, which is rescued by Ssrp1 re-introduction; Usp7 deubiquitinates H2Bub at these loci to repress MERVL-fused gene expression.","method":"Co-immunoprecipitation (SSRP1-Usp7), ChIP, RNA-seq, SSRP1 rescue experiment, siRNA knockdown of Usp7","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP, ChIP, RNA-seq, and rescue experiment; single lab, multiple methods","pmids":["32894293"],"is_preprint":false},{"year":2018,"finding":"FACT inhibition (SPT16 CRISPR deletion or small molecule inhibitor) blocks reprogramming of fibroblasts to iPSCs at an early step without affecting fibroblast viability or proliferation; FACT is not required for maintenance of established pluripotency (core pluripotency gene expression unaffected), but trypsinization and passaging transiently reintroduces a FACT requirement, suggesting FACT promotes transitions between stable chromatin states rather than acting as a constitutive elongation factor.","method":"CRISPR-mediated SPT16 deletion, small-molecule FACT inhibitor, iPSC reprogramming assay, gene expression analysis","journal":"Stem cells and development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR KO and chemical inhibitor with specific functional reprogramming phenotype; single lab, two orthogonal perturbations","pmids":["30319048"],"is_preprint":false}],"current_model":"SUPT16H (SPT16) is the large subunit of the FACT histone chaperone complex (together with SSRP1), which facilitates chromatin transcription by engaging nucleosomal DNA and all four histone variants: SPT16 destabilizes nucleosomes by displacing H2A-H2B dimers (with its C-terminal domain acting as a placeholder for DNA while tethering H2A-H2B), while SSRP1 maintains nucleosome integrity by anchoring H3-H4; the complex uses these opposing activities to both remove and reassemble nucleosomes during RNA Pol II (and Pol I/III) transcription elongation, DNA replication-coupled nucleosome assembly, and DNA double-strand break repair, while also maintaining chromatin architecture to support promoter-proximal Pol II pausing in vivo."},"narrative":{"mechanistic_narrative":"SUPT16H (SPT16) is the large subunit of the heterodimeric FACT histone chaperone, which partners with SSRP1 to manage nucleosome dynamics during transcription, DNA replication, and repair [PMID:10421373, PMID:1922073]. FACT engages nucleosomal DNA and all four core histones, and SPT16 and SSRP1 perform opposing but coordinated activities: SPT16 destabilizes nucleosomes by displacing H2A-H2B dimers — with its C-terminal domain serving as a placeholder for DNA while tethering H2A-H2B — whereas SSRP1 holds the H3-H4 tetramer on DNA and promotes dimer redeposition, allowing the complex to both disassemble and reassemble nucleosomes [PMID:31775157, PMID:30029006]. The conserved SPT16 N-terminal domain adopts an enzymatically inactive aminopeptidase fold that binds the H3-H4 globular core and tails [PMID:18579787]. In transcription, FACT acts at both initiation, by promoting TBP binding within a nucleosomal TATA box [PMID:15987999], and elongation, by binding the partially unraveled nucleosome generated as RNA Pol II transits and by facilitating reassembly upstream [PMID:33846633]; in vivo it maintains the +1 nucleosome required for promoter-proximal Pol II pausing and productive elongation [PMID:38810649], and supports Pol I and Pol III transcription as well [PMID:19214185]. FACT couples nucleosome assembly to DNA replication by depositing newly synthesized H3-H4 and recruits to the fork through a direct SPT16 N-terminal interaction with the fork-protection factor Tof1 [PMID:26804921, PMID:35061899], and is essential to sustain MCM2-7 helicase retention and ATR/CHK1 checkpoint signaling under replication stress [PMID:32533099]. In DNA double-strand break repair, SUPT16H directly binds RNF20 to drive H2B ubiquitylation, chromatin relaxation, and end resection [PMID:22031019, PMID:24357716]. FACT activity is further integrated with histone ubiquitin turnover through stimulation of the deubiquitinases Ubp10 and Usp7 [PMID:30681413, PMID:32894293] and with higher-order genome organization via a direct interaction with cohesin that supports TAD formation [PMID:31582854]. At specific loci FACT acts repressively, acting as a barrier to cell-fate reprogramming [PMID:30078731, PMID:30319048] and supporting stress-responsive gene induction downstream of TFEB/TFE3 [PMID:35230915].","teleology":[{"year":1991,"claim":"Established SUPT16H's yeast ortholog as an essential gene linking transcription to the cell cycle, the first functional anchor for the gene.","evidence":"Null and temperature-sensitive alleles with genetic suppression and epistasis in S. cerevisiae","pmids":["1922073"],"confidence":"High","gaps":["Did not define a biochemical activity or partner","Mechanistic basis of transcriptional and cell-cycle defects unresolved"]},{"year":1999,"claim":"Defined FACT as the SPT16-SSRP1 heterodimer and showed it is a chromatin-specific elongation factor acting by nucleosome disassembly, establishing the molecular identity and core activity.","evidence":"Biochemical purification, reconstituted in vitro chromatin transcription, nucleosome/H2A-H2B binding, histone crosslinking","pmids":["10421373"],"confidence":"High","gaps":["Structural basis of nucleosome engagement unknown","How disassembly is coupled to reassembly not addressed"]},{"year":2005,"claim":"Extended FACT function to transcription initiation by showing SPT16 promotes TBP loading on nucleosomal promoters, broadening its role beyond elongation.","evidence":"In vitro TBP-nucleosome reconstitution, synthetic lethality, and ChIP in yeast","pmids":["15987999"],"confidence":"High","gaps":["Mechanism of TBP-facilitating nucleosome remodeling not structurally defined","Generality across promoters in metazoans untested"]},{"year":2008,"claim":"Identified the SPT16 N-terminal domain as a structurally defined H3-H4 binding module, assigning histone-binding function to a specific region.","evidence":"2.1 Å crystal structure of Spt16-N with mutagenesis and in vitro binding (fission yeast)","pmids":["18579787"],"confidence":"High","gaps":["Role of H3-H4 binding within the intact nucleosome cycle not shown","Functional necessity of the domain in vivo not defined here"]},{"year":2009,"claim":"Showed FACT operates beyond Pol II, co-purifying with and facilitating Pol I and Pol III transcription, generalizing its chromatin-elongation role.","evidence":"Co-IP, ChIP at rRNA repeats, siRNA knockdown, run-on assay in mammalian cells","pmids":["19214185"],"confidence":"High","gaps":["Whether the SPT16 nucleosome mechanism is identical across polymerases not resolved"]},{"year":2009,"claim":"Demonstrated FACT-dependent nucleosome eviction at a promoter and its requirement for coactivator re-recruitment, linking chromatin disassembly to gene activation in vivo.","evidence":"Cell-cycle-resolved ChIP and genetic epistasis at the yeast HO promoter","pmids":["19481521"],"confidence":"Medium","gaps":["Single-locus study; genome-wide generality not established here","Direct SPT16 vs SSRP1 contributions not separated"]},{"year":2011,"claim":"Connected SUPT16H to DNA double-strand break repair by showing it is required for RNF20-mediated H2B ubiquitylation and repair-protein loading, opening a genome-stability role.","evidence":"siRNA knockdown, co-IP, γH2AX/repair foci, HR reporter, IR sensitivity in human cells","pmids":["22031019"],"confidence":"Medium","gaps":["Direct vs indirect role of SPT16 in RNF20 recruitment not fully resolved","Single-lab phenotypes"]},{"year":2013,"claim":"Confirmed and refined the DSB role, establishing direct SUPT16H-RNF20 binding and FACT-driven chromatin relaxation as upstream of efficient homologous recombination.","evidence":"Co-IP, foci imaging, HR reporter, clonogenic survival, rescue by enforced nucleosome relaxation","pmids":["24357716"],"confidence":"Medium","gaps":["Structural detail of the SPT16-RNF20 interface unknown","How FACT senses DSB sites not defined"]},{"year":2016,"claim":"Placed FACT in replication-coupled nucleosome assembly, showing SPT16 H3-H4 binding drives deposition of new histones in concert with Rtt106 and the H3K56ac mark.","evidence":"Genetic epistasis, mutant allele binding assays, co-IP, histone deposition assay in yeast","pmids":["26804921"],"confidence":"High","gaps":["Order of FACT vs CAF-1/Rtt106 handoff during replication not fully ordered"]},{"year":2018,"claim":"Resolved the division of labor between subunits, showing SPT16 destabilizes nucleosomes by dimer displacement while SSRP1 preserves the H3-H4 tetramer — the mechanistic core of FACT activity.","evidence":"Single-nucleosome FRET and biochemical subunit dissection","pmids":["30029006"],"confidence":"High","gaps":["How the two opposing activities are temporally coordinated in vivo not shown"]},{"year":2018,"claim":"Revealed a repressive, transition-specific function by showing FACT is a barrier to cell-fate reprogramming, distinguishing it from a purely constitutive elongation factor.","evidence":"C. elegans genetic screen, human fibroblast knockdown, iPSC reprogramming, RNA-seq/ChIP-seq; CRISPR SPT16 deletion and chemical inhibition","pmids":["30078731","30319048"],"confidence":"Medium","gaps":["Molecular basis of locus-specific repression vs activation unclear","Why FACT requirement is transient during state transitions undefined"]},{"year":2019,"claim":"Provided the structural mechanism of nucleosome engagement, showing FACT CTDs gate DNA binding and SPT16 CTD acts as a DNA placeholder tethering H2A-H2B.","evidence":"Two cryo-EM structures of human FACT-subnucleosome plus HDX-MS and biochemistry","pmids":["31775157"],"confidence":"High","gaps":["Dynamics of conformational switching in real time not captured","Structure on a fully transcribing complex not in this study"]},{"year":2019,"claim":"Integrated FACT with histone-ubiquitin turnover and chromatin homeostasis, linking it to deubiquitinase stimulation, antisense suppression, histone recycling, and genome architecture.","evidence":"In vitro deubiquitination, genetic epistasis, RNA-seq/ChIP-seq/nucleosome mapping, co-IP and Hi-C across yeast and human studies","pmids":["30681413","31837996","31365865","31582854"],"confidence":"High","gaps":["Whether cohesin and H2Bub effects share a common SPT16 surface unknown","Direct vs indirect contribution to TAD formation not separated"]},{"year":2019,"claim":"Connected FACT to transcription-coupled DSB responses and DNA-structure sensing, with OTUD5-SPT16 driving Pol II arrest and SSRP1 recognizing Z-DNA-prone sequences to trigger p53.","evidence":"DUB RNAi screen, co-IP, RNA synthesis assays; in vitro DNA binding and curaxin ChIP with p53 readout","pmids":["30508113","28082391"],"confidence":"Medium","gaps":["Whether SPT16 or SSRP1 is the primary structural sensor not resolved","Physiological prevalence of Z-DNA sensing unclear"]},{"year":2020,"claim":"Established FACT as essential for surviving replication stress by maintaining MCM2-7 retention and enabling ATR/CHK1 checkpoint activation.","evidence":"Knockdown/knockout, chromatin fractionation, RPA imaging, checkpoint phospho-analysis, DNA fiber assay in mammalian cells","pmids":["32533099"],"confidence":"Medium","gaps":["Direct vs chromatin-mediated effect on MCM retention not distinguished","Single-lab findings"]},{"year":2021,"claim":"Visualized FACT acting during active Pol II transcription, showing it binds partially unraveled nucleosomes and excludes Chd1/Spt5 to position reassembly upstream.","evidence":"Cryo-EM of yeast Pol II-Spt4/5-nucleosome complexes and in vitro transcription reconstitution","pmids":["33846633"],"confidence":"High","gaps":["Kinetic coupling between Pol II passage and FACT reassembly not measured"]},{"year":2022,"claim":"Defined domain-specific recruitment of FACT to the replication fork via SPT16 N-terminus-Tof1 interaction, and showed nucleosome reorganization requires the middle and C-terminal domains.","evidence":"Single-molecule FRET, structure-guided pulldowns, in vitro chromatin replication","pmids":["35061899"],"confidence":"High","gaps":["Whether the analogous SPT16-fork interaction operates in human cells not shown here"]},{"year":2022,"claim":"Linked FACT to metabolic and stress signaling, with PKM2-derived pyruvate binding SSRP1 to enhance γH2AX chromatin loading, and FACT acting downstream of TFEB/TFE3 to remodel stress-gene promoters.","evidence":"Co-IP, in vitro binding, γH2AX loading assays, phospho-mutant analysis; 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SSRP1 proteins; FACT specifically interacts with nucleosomes and histone H2A/H2B dimers and functions as a chromatin-specific transcription elongation factor required for transcription of chromatin templates in vitro; FACT activity is abrogated by covalent crosslinking of nucleosomal histones, indicating it works by promoting nucleosome disassembly.\",\n      \"method\": \"Biochemical purification, reconstituted in vitro transcription on chromatin templates, direct binding assays (nucleosome and H2A/H2B interaction), crosslinking experiments\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro chromatin transcription assay, direct binding to nucleosomes/H2A-H2B demonstrated, functional abrogation by crosslinking; foundational paper replicated by many subsequent studies\",\n      \"pmids\": [\"10421373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"SPT16/CDC68 (yeast orthologue of SUPT16H) is an essential gene in S. cerevisiae required for normal transcription at multiple loci; temperature-sensitive spt16 alleles suppress delta insertion mutations and upstream activating sequence deletions, demonstrating a role in promoter function; SPT16 is identical to CDC68, previously shown to be required for passage through cell-cycle START, but transcriptional effects of spt16 mutations are at least partially independent of cell-cycle arrest.\",\n      \"method\": \"Null mutation construction, temperature-sensitive allele isolation, genetic suppression assays, epistasis analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic epistasis experiments in yeast, null and conditional alleles, replicated by accompanying paper; foundational genetic characterization\",\n      \"pmids\": [\"1922073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The N-terminal 'peptidase homology' domain of fission yeast Spt16 (Spt16-N) is a histone H3-H4 binding module; crystal structure at 2.1 Å reveals an aminopeptidase P fold that has lost enzymatic activity but directly binds the globular core domains and N-terminal tails of H3-H4; mutations in a conserved surface pocket in Spt16-N or posttranslational modification of the H4 tail reduce interaction in vitro.\",\n      \"method\": \"X-ray crystallography (2.1 Å), biochemical binding assays, site-directed mutagenesis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus mutagenesis and in vitro binding assays in a single rigorous study; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"18579787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Cryo-EM structures of human FACT (SPT16/SSRP1) in complex with partially assembled subnucleosomes reveal: (1) FACT engages extensively with nucleosomal DNA and all histone variants; (2) the C-terminal domains (CTDs) of both SPT16 and SSRP1 protect the DNA-binding surface; (3) interaction with H2A-H2B releases this inhibition allowing FACT-H2A-H2B to dock onto a DNA/H3-H4 complex; (4) SPT16 CTD acts as a placeholder for DNA by tethering H2A-H2B; (5) SSRP1 can adopt two conformations depending on whether a second H2A-H2B dimer is present. This mechanism facilitates H2A-H2B dimer removal, stabilizes subnucleosomal intermediates, and promotes reassembly.\",\n      \"method\": \"Cryo-electron microscopy (two structures), hydrogen-deuterium exchange mass spectrometry, biochemical binding assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — two independent cryo-EM structures with supporting HDX-MS and biochemical data; multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"31775157\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SPT16 (large subunit of FACT) destabilizes the nucleosome by displacing H2A/H2B dimers at the single-nucleosome level, while SSRP1 (small subunit) maintains nucleosome integrity by holding the H3/H4 tetramer on DNA and promoting deposition of H2A/H2B dimers; the two subunits thus play opposing but coordinated roles in nucleosome remodeling.\",\n      \"method\": \"Single-nucleosome FRET, biochemical reconstitution, subunit-specific functional dissection\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — single-molecule FRET reconstitution with biochemical dissection of individual subunit functions; single lab, multiple orthogonal approaches\",\n      \"pmids\": [\"30029006\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-EM structures of transcribing yeast RNA Pol II-Spt4/5-nucleosome complexes show that FACT binds a partially unraveled nucleosome generated during Pol II transcription, excludes Chd1 and Spt5, and is positioned to facilitate nucleosome reassembly upstream; biochemically, FACT facilitates Pol II transcription through a nucleosome when Spt4/5 and TFIIS are present.\",\n      \"method\": \"Cryo-electron microscopy, in vitro transcription reconstitution on chromatin templates\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structures plus in vitro reconstituted transcription assay; multiple orthogonal methods\",\n      \"pmids\": [\"33846633\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"FACT (SSRP1 and SPT16 subunits) co-purifies and co-immunoprecipitates with mammalian RNA Pol I complexes; SSRP1 is detectable at rRNA gene repeats by ChIP; siRNA knockdown of FACT subunits reduces 47S pre-rRNA levels without affecting synthesis of the first 40 nt of rRNA, placing FACT function specifically at Pol I elongation through chromatin. FACT also associates with Pol III complexes and facilitates Pol III-transcribed gene expression.\",\n      \"method\": \"Co-immunoprecipitation, chromatin immunoprecipitation (ChIP), siRNA knockdown, run-on transcription assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP, ChIP localization, and functional siRNA knockdown with specific elongation phenotype; multiple orthogonal methods in one study\",\n      \"pmids\": [\"19214185\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Yeast FACT (yFACT) promotes TBP binding to a TATA box within a reconstituted nucleosome in a TFIIA-dependent manner in vitro; in vivo, certain spt16 mutations are synthetically lethal with TBP and TFIIA (TOA2) mutants, and spt16 mutations reduce TBP binding to promoters by ChIP, establishing a role for SPT16 in transcription initiation as well as elongation.\",\n      \"method\": \"In vitro TBP-nucleosome binding reconstitution, genetic synthetic lethality, chromatin immunoprecipitation (ChIP)\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro reconstitution plus genetic epistasis plus ChIP; multiple orthogonal methods in one study\",\n      \"pmids\": [\"15987999\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"At the yeast HO promoter, FACT (SPT16-containing complex) is required for nucleosome eviction at distinct promoter regions; FACT and Asf1 bind upstream HO promoter elements before transcription initiation and are both required for re-recruitment of Swi/Snf, SAGA, and Mediator coactivators to promoter-proximal regions.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), genetic epistasis with chromatin modifier mutants, cell-cycle-resolved ChIP analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP-based dissection of nucleosome dynamics and coactivator recruitment at a specific promoter; single lab, multiple gene deletions and ChIP analyses\",\n      \"pmids\": [\"19481521\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"FACT (Spt16-Pob3 in yeast) promotes newly synthesized histone H3-H4 deposition during DNA replication-coupled nucleosome assembly; an spt16 allele (spt16-m) defective in H3-H4 binding impairs their deposition; FACT physically associates with Rtt106 and the H3K56 acetylation mark on newly synthesized H3 modulates this interaction; FACT shows synthetic defects with CAF-1 and Rtt106.\",\n      \"method\": \"Genetic epistasis (synthetic lethality), in vitro H3-H4 binding assays, co-immunoprecipitation, site-directed mutagenesis, histone deposition assay\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — reconstituted binding assays with mutant allele, co-IP with Rtt106, genetic epistasis; multiple orthogonal approaches in one study\",\n      \"pmids\": [\"26804921\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SUPT16H (SPT16, a FACT subunit) is required for RNF20-mediated H2B ubiquitylation at sites of DNA double-strand breaks; depletion of SUPT16H causes defective accumulation of repair proteins (RAD51, BRCA1), decreased H3K56ac, sustained γH2AX phosphorylation, impaired DNA end resection, delayed DSB repair, and decreased recruitment of SNF2h; SUPT16H directly binds RNF20 in vivo; PAF1 is dispensable for DNA damage-induced SUPT16H-RNF20 interaction.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, γH2AX foci imaging, H3K56ac quantification, homologous recombination reporter assay, ionizing radiation sensitivity\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple siRNA knockdowns phenocopying each other, co-IP, and functional repair assays; single lab, multiple readouts\",\n      \"pmids\": [\"22031019\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SUPT16H (FACT) is required for RNF20 recruitment to DNA double-strand break sites and subsequent H2B ubiquitylation; SUPT16H directly binds RNF20 in vivo and is required for SNF2h accumulation and chromatin relaxation at DSBs; SUPT16H depletion causes radiation and mitomycin-C sensitivity and decreased homologous recombination activity; enforced nucleosome relaxation counteracts SUPT16H-deficient phenotypes.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, immunofluorescence foci assays, HR reporter assay, clonogenic survival assay\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus functional HR and repair assays; single lab, multiple orthogonal readouts\",\n      \"pmids\": [\"24357716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"FACT (Spt16 subunit) forms a stable ~600 kDa complex with the kinase Nek9 in interphase nuclei; when complexed with FACT, Nek9 exhibits elevated phosphorylation on Thr210 (activation loop); Nek9 RNAi causes defects in G1 and S phase progression, phenotypically linked to the phospho-Nek9-FACT complex formation.\",\n      \"method\": \"Co-immunoprecipitation, size-exclusion chromatography, phosphorylation analysis, RNA interference cell-cycle analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — stable complex identified by co-IP and gel filtration, phosphorylation state characterized, RNAi phenotype; single lab, single co-IP with supporting functional data\",\n      \"pmids\": [\"14660563\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Domain organization of yeast FACT: FACT integrity depends on Pob3 interactions with the Spt16 Mid domain; the conserved Spt16 N-terminal domain (NTD) is dispensable for normal growth but becomes important under replication stress conditions; genetic interactions suggest some Spt16 NTD functions are partially redundant within FACT.\",\n      \"method\": \"Genetic analysis (deletion alleles, synthetic lethality), biochemical fractionation\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic domain dissection with multiple alleles and biochemical fractionation; single lab\",\n      \"pmids\": [\"15520471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"FACT (via its SSRP1 subunit/CID domain) binds Z-DNA or DNA in transition from B to Z form in cells treated with curaxin; purified SSRP1 CID domain binds methylated alternating purine/pyrimidine DNA (prone to Z-DNA transition) more strongly than other DNA types in vitro; FACT binding to these alternative DNA structure regions triggers a p53 response, positioning FACT as a sensor of DNA torsional stress.\",\n      \"method\": \"ChIP after curaxin treatment, in vitro DNA binding assays with purified SSRP1/CID, p53 response assay\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro binding assay plus in-cell ChIP localization plus functional p53 readout; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"28082391\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SUPT16H (SPT16) interacts with HIV-1 Tat protein (but not SSRP1); both SUPT16H and SSRP1 are recruited to the HIV-1 LTR promoter; SUPT16H presence interferes with Cyclin T1 (P-TEFb subunit) association with the Tat-LTR axis; depletion of SUPT16H or SSRP1 enhances Tat-mediated LTR activity, affects transcriptional initiation and elongation, and spontaneously reverses HIV-1 latency in cell models.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, RNAi knockdown, HIV-1 latency reactivation assay, LTR reporter assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP, ChIP, and functional knockdown with latency phenotype; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"26378236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FACT stimulates Ubp10 deubiquitinase activity specifically on nucleosome substrates (not other substrates); a FACT mutant strain shows elevated H2B monoubiquitination in vivo; combination of FACT mutants with deletion of Ubp10 (but not Ubp8) confers increased sensitivity to hydroxyurea and activates cryptic transcription, indicating FACT and Ubp10 coordinate nucleosome assembly during DNA replication and transcription.\",\n      \"method\": \"In vitro deubiquitination assay with reconstituted nucleosomes, H2B-Ub immunoblotting in FACT mutant strains, genetic epistasis (double mutants), cryptic transcription reporter assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstituted deubiquitination assay plus in vivo H2B-Ub measurement plus genetic epistasis; multiple orthogonal methods in one study\",\n      \"pmids\": [\"30681413\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FACT globally represses antisense transcripts near the 5' end of genes in S. pombe; H2B ubiquitination (H2Bub) is required for FACT activity in genic regions—in the H2Bub mutant, FACT binding to chromatin is altered and its association with histones stabilized, leading to reduction of genic nucleosomes; FACT depletion globally restores nucleosomes lost in the H2Bub mutant; FACT (specifically Spt16 subunit absent Pob3) also controls the 3' end processing of genes and maintains nucleosomes in subtelomeric regions required for their compaction.\",\n      \"method\": \"RNA-seq, ChIP-seq, genome-wide nucleosome mapping, genetic (H2Bub mutant and FACT depletion), co-immunoprecipitation, microscopy\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genomics, genetic epistasis, biochemistry, and microscopy across multiple orthogonal approaches; replicated across conditions\",\n      \"pmids\": [\"31837996\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FACT mediates cohesin function on chromatin: FACT interacts directly with cohesin, is dynamically required for cohesin localization on chromatin; depletion of FACT in metaphase cells prevents cohesin accumulation at pericentric regions and reduces binding on chromosome arms; FACT depletion reduces cohesin-dependent TAD-like structures in both G1 and metaphase chromosomes by Hi-C, although sister chromatid cohesion itself is intact.\",\n      \"method\": \"Co-immunoprecipitation (FACT-cohesin), ChIP-seq (cohesin localization), Hi-C (TAD analysis), conditional FACT depletion\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct co-IP between FACT and cohesin, ChIP-seq, Hi-C, conditional depletion; multiple orthogonal methods in one study\",\n      \"pmids\": [\"31582854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"OTUD5 deubiquitinase interacts with FACT component SPT16 and antagonizes H2A deposition at DNA double-strand break lesions; OTUD5-SPT16 interaction (along with OTUD5-UBR5 interaction) is required for arresting RNA Pol II elongation at DSB lesions; a cancer-associated missense mutation in OTUD5 UIM abrogates FACT association and Pol II arrest.\",\n      \"method\": \"DUB RNAi screen, co-immunoprecipitation, immunofluorescence, RNA synthesis assay at DSBs\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP, RNAi screen validation, and functional Pol II arrest assay; single lab, multiple readouts\",\n      \"pmids\": [\"30508113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FACT and Spt6 are required for local recycling of modified histones during transcription in S. cerevisiae; disruption of FACT or Spt6 causes nucleosome loss that is partially compensated by non-transcription-coupled chaperones; in the absence of functional FACT or Spt6, transcription-evicted modified histones are randomly incorporated, scrambling epigenomic information.\",\n      \"method\": \"ChIP-seq for histone modifications in FACT/Spt6 mutant strains, nucleosome mapping, genetic analysis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genome-wide ChIP-seq in defined mutants with mechanistic interpretation; single lab\",\n      \"pmids\": [\"31365865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"FACT acts as a barrier to cell fate reprogramming in C. elegans and humans: FACT depletion in C. elegans identified in a genetic screen as maintaining cell identity; FACT depletion enhances reprogramming of human fibroblasts to iPSCs; a subset of FACT-occupied genes (including reprogramming-promoting factors) shows increased expression upon FACT depletion, revealing a repressive function of FACT at specific loci.\",\n      \"method\": \"Genetic screen (C. elegans), siRNA/shRNA knockdown, iPSC reprogramming efficiency assay, RNA-seq, ChIP-seq\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic screen plus mammalian knockdown with reprogramming phenotype and RNA-seq; cross-species conservation; single lab\",\n      \"pmids\": [\"30078731\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"FACT is essential to overcome replication stress in mammalian cells: in the absence of FACT during replication stress, the MCM2-7 helicase dissociates from chromatin, resulting in absence of ssDNA accumulation, RPA binding, and ATR/CHK1 checkpoint activation; without this response, stalled replication forks are not stabilized, new origin firing is not prevented, and DNA damage and cell death accumulate.\",\n      \"method\": \"Genetic knockdown/knockout, chromatin fractionation (MCM2-7 dissociation), RPA immunofluorescence, ATR/CHK1 phosphorylation analysis, DNA fiber assay, hydroxyurea/APH treatment\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal assays (chromatin fractionation, checkpoint signaling, DNA fiber) with specific molecular mechanism; single lab\",\n      \"pmids\": [\"32533099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FACT (SSRP1 and SUPT16H) interacts with transcription factors TFEB and TFE3 in the nucleus upon nutrient deprivation or oxidative stress; FACT depletion (siRNA or curaxin inhibitor) does not affect TFEB activation, stability, or promoter binding, but severely impairs induction of antioxidant and lysosomal target genes; FACT is required downstream of TFEB/TFE3 binding for chromatin remodeling at stress-responsive gene promoters.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, curaxin inhibitor treatment, RT-qPCR, ChIP\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP, knockdown and inhibitor with gene expression readouts, ChIP; single lab, multiple approaches\",\n      \"pmids\": [\"35230915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Recruitment of FACT to the replication fork requires the N-terminal domain of Spt16, which directly interacts with the fork protection complex subunit Tof1; single-molecule FRET demonstrates that nucleosomal DNA reorganization by FACT requires coordinated engagement by the middle and C-terminal domains of Spt16 and Pob3 (but not Spt16 N-terminus); this Tof1-Spt16 NTD interaction is required for robust in vitro chromatin replication.\",\n      \"method\": \"Single-molecule FRET, structure-guided pulldowns, in vitro chromatin replication assay\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — single-molecule FRET reconstitution, pulldown binding assay, in vitro replication assay; multiple orthogonal methods in one study\",\n      \"pmids\": [\"35061899\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Pyruvate produced by PKM2 directly binds SSRP1 subunit of the FACT complex, increasing FACT association with γH2AX and facilitating FACT-mediated chromatin loading of γH2AX to promote DNA repair; PKM2 is phosphorylated at S222 upon DNA damage and interacts with the FACT complex (SPT16 and SSRP1); exogenous pyruvate supplementation is sufficient to enhance FACT-mediated γH2AX chromatin loading.\",\n      \"method\": \"Co-immunoprecipitation, in vitro binding assay (pyruvate-SSRP1), γH2AX chromatin loading assay, PKM2 phospho-mutant analysis, clonogenic survival\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP, in vitro binding, functional γH2AX loading assay; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"35048565\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Rapid depletion of FACT from human cells in vivo destabilizes chromatin and leads to: (1) defective promoter-proximal RNA Pol II pausing dependent on the +1 nucleosome maintained by FACT; (2) elongation defects; (3) increased premature termination of Pol II; demonstrating that FACT maintains chromatin architecture in vivo to support pausing and productive elongation.\",\n      \"method\": \"Rapid auxin-inducible degron (AID) FACT depletion, multi-omics (ChIP-seq, PRO-seq, RNA-seq, ATAC-seq/MNase-seq)\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — rapid in vivo depletion with multi-omics readouts identifying specific mechanistic defects; multiple orthogonal genome-wide methods\",\n      \"pmids\": [\"38810649\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"FACT (SSRP1 subunit) recruits H2B deubiquitinase Usp7 to SSRP1 target genes in mouse ESCs; Ssrp1 interacts with MERVL retrotransposon sequences and suppresses cryptic MERVL-derived transcription; loss of Ssrp1 activates MERVL ERVs, which is rescued by Ssrp1 re-introduction; Usp7 deubiquitinates H2Bub at these loci to repress MERVL-fused gene expression.\",\n      \"method\": \"Co-immunoprecipitation (SSRP1-Usp7), ChIP, RNA-seq, SSRP1 rescue experiment, siRNA knockdown of Usp7\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP, ChIP, RNA-seq, and rescue experiment; single lab, multiple methods\",\n      \"pmids\": [\"32894293\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"FACT inhibition (SPT16 CRISPR deletion or small molecule inhibitor) blocks reprogramming of fibroblasts to iPSCs at an early step without affecting fibroblast viability or proliferation; FACT is not required for maintenance of established pluripotency (core pluripotency gene expression unaffected), but trypsinization and passaging transiently reintroduces a FACT requirement, suggesting FACT promotes transitions between stable chromatin states rather than acting as a constitutive elongation factor.\",\n      \"method\": \"CRISPR-mediated SPT16 deletion, small-molecule FACT inhibitor, iPSC reprogramming assay, gene expression analysis\",\n      \"journal\": \"Stem cells and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR KO and chemical inhibitor with specific functional reprogramming phenotype; single lab, two orthogonal perturbations\",\n      \"pmids\": [\"30319048\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SUPT16H (SPT16) is the large subunit of the FACT histone chaperone complex (together with SSRP1), which facilitates chromatin transcription by engaging nucleosomal DNA and all four histone variants: SPT16 destabilizes nucleosomes by displacing H2A-H2B dimers (with its C-terminal domain acting as a placeholder for DNA while tethering H2A-H2B), while SSRP1 maintains nucleosome integrity by anchoring H3-H4; the complex uses these opposing activities to both remove and reassemble nucleosomes during RNA Pol II (and Pol I/III) transcription elongation, DNA replication-coupled nucleosome assembly, and DNA double-strand break repair, while also maintaining chromatin architecture to support promoter-proximal Pol II pausing in vivo.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SUPT16H (SPT16) is the large subunit of the heterodimeric FACT histone chaperone, which partners with SSRP1 to manage nucleosome dynamics during transcription, DNA replication, and repair [#0, #1]. FACT engages nucleosomal DNA and all four core histones, and SPT16 and SSRP1 perform opposing but coordinated activities: SPT16 destabilizes nucleosomes by displacing H2A-H2B dimers — with its C-terminal domain serving as a placeholder for DNA while tethering H2A-H2B — whereas SSRP1 holds the H3-H4 tetramer on DNA and promotes dimer redeposition, allowing the complex to both disassemble and reassemble nucleosomes [#3, #4]. The conserved SPT16 N-terminal domain adopts an enzymatically inactive aminopeptidase fold that binds the H3-H4 globular core and tails [#2]. In transcription, FACT acts at both initiation, by promoting TBP binding within a nucleosomal TATA box [#7], and elongation, by binding the partially unraveled nucleosome generated as RNA Pol II transits and by facilitating reassembly upstream [#5]; in vivo it maintains the +1 nucleosome required for promoter-proximal Pol II pausing and productive elongation [#26], and supports Pol I and Pol III transcription as well [#6]. FACT couples nucleosome assembly to DNA replication by depositing newly synthesized H3-H4 and recruits to the fork through a direct SPT16 N-terminal interaction with the fork-protection factor Tof1 [#9, #24], and is essential to sustain MCM2-7 helicase retention and ATR/CHK1 checkpoint signaling under replication stress [#22]. In DNA double-strand break repair, SUPT16H directly binds RNF20 to drive H2B ubiquitylation, chromatin relaxation, and end resection [#10, #11]. FACT activity is further integrated with histone ubiquitin turnover through stimulation of the deubiquitinases Ubp10 and Usp7 [#16, #27] and with higher-order genome organization via a direct interaction with cohesin that supports TAD formation [#18]. At specific loci FACT acts repressively, acting as a barrier to cell-fate reprogramming [#21, #28] and supporting stress-responsive gene induction downstream of TFEB/TFE3 [#23].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Established SUPT16H's yeast ortholog as an essential gene linking transcription to the cell cycle, the first functional anchor for the gene.\",\n      \"evidence\": \"Null and temperature-sensitive alleles with genetic suppression and epistasis in S. cerevisiae\",\n      \"pmids\": [\"1922073\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define a biochemical activity or partner\", \"Mechanistic basis of transcriptional and cell-cycle defects unresolved\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Defined FACT as the SPT16-SSRP1 heterodimer and showed it is a chromatin-specific elongation factor acting by nucleosome disassembly, establishing the molecular identity and core activity.\",\n      \"evidence\": \"Biochemical purification, reconstituted in vitro chromatin transcription, nucleosome/H2A-H2B binding, histone crosslinking\",\n      \"pmids\": [\"10421373\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of nucleosome engagement unknown\", \"How disassembly is coupled to reassembly not addressed\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Extended FACT function to transcription initiation by showing SPT16 promotes TBP loading on nucleosomal promoters, broadening its role beyond elongation.\",\n      \"evidence\": \"In vitro TBP-nucleosome reconstitution, synthetic lethality, and ChIP in yeast\",\n      \"pmids\": [\"15987999\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of TBP-facilitating nucleosome remodeling not structurally defined\", \"Generality across promoters in metazoans untested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identified the SPT16 N-terminal domain as a structurally defined H3-H4 binding module, assigning histone-binding function to a specific region.\",\n      \"evidence\": \"2.1 Å crystal structure of Spt16-N with mutagenesis and in vitro binding (fission yeast)\",\n      \"pmids\": [\"18579787\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Role of H3-H4 binding within the intact nucleosome cycle not shown\", \"Functional necessity of the domain in vivo not defined here\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Showed FACT operates beyond Pol II, co-purifying with and facilitating Pol I and Pol III transcription, generalizing its chromatin-elongation role.\",\n      \"evidence\": \"Co-IP, ChIP at rRNA repeats, siRNA knockdown, run-on assay in mammalian cells\",\n      \"pmids\": [\"19214185\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the SPT16 nucleosome mechanism is identical across polymerases not resolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrated FACT-dependent nucleosome eviction at a promoter and its requirement for coactivator re-recruitment, linking chromatin disassembly to gene activation in vivo.\",\n      \"evidence\": \"Cell-cycle-resolved ChIP and genetic epistasis at the yeast HO promoter\",\n      \"pmids\": [\"19481521\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-locus study; genome-wide generality not established here\", \"Direct SPT16 vs SSRP1 contributions not separated\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Connected SUPT16H to DNA double-strand break repair by showing it is required for RNF20-mediated H2B ubiquitylation and repair-protein loading, opening a genome-stability role.\",\n      \"evidence\": \"siRNA knockdown, co-IP, γH2AX/repair foci, HR reporter, IR sensitivity in human cells\",\n      \"pmids\": [\"22031019\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect role of SPT16 in RNF20 recruitment not fully resolved\", \"Single-lab phenotypes\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Confirmed and refined the DSB role, establishing direct SUPT16H-RNF20 binding and FACT-driven chromatin relaxation as upstream of efficient homologous recombination.\",\n      \"evidence\": \"Co-IP, foci imaging, HR reporter, clonogenic survival, rescue by enforced nucleosome relaxation\",\n      \"pmids\": [\"24357716\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural detail of the SPT16-RNF20 interface unknown\", \"How FACT senses DSB sites not defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Placed FACT in replication-coupled nucleosome assembly, showing SPT16 H3-H4 binding drives deposition of new histones in concert with Rtt106 and the H3K56ac mark.\",\n      \"evidence\": \"Genetic epistasis, mutant allele binding assays, co-IP, histone deposition assay in yeast\",\n      \"pmids\": [\"26804921\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Order of FACT vs CAF-1/Rtt106 handoff during replication not fully ordered\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Resolved the division of labor between subunits, showing SPT16 destabilizes nucleosomes by dimer displacement while SSRP1 preserves the H3-H4 tetramer — the mechanistic core of FACT activity.\",\n      \"evidence\": \"Single-nucleosome FRET and biochemical subunit dissection\",\n      \"pmids\": [\"30029006\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the two opposing activities are temporally coordinated in vivo not shown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Revealed a repressive, transition-specific function by showing FACT is a barrier to cell-fate reprogramming, distinguishing it from a purely constitutive elongation factor.\",\n      \"evidence\": \"C. elegans genetic screen, human fibroblast knockdown, iPSC reprogramming, RNA-seq/ChIP-seq; CRISPR SPT16 deletion and chemical inhibition\",\n      \"pmids\": [\"30078731\", \"30319048\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of locus-specific repression vs activation unclear\", \"Why FACT requirement is transient during state transitions undefined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Provided the structural mechanism of nucleosome engagement, showing FACT CTDs gate DNA binding and SPT16 CTD acts as a DNA placeholder tethering H2A-H2B.\",\n      \"evidence\": \"Two cryo-EM structures of human FACT-subnucleosome plus HDX-MS and biochemistry\",\n      \"pmids\": [\"31775157\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Dynamics of conformational switching in real time not captured\", \"Structure on a fully transcribing complex not in this study\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Integrated FACT with histone-ubiquitin turnover and chromatin homeostasis, linking it to deubiquitinase stimulation, antisense suppression, histone recycling, and genome architecture.\",\n      \"evidence\": \"In vitro deubiquitination, genetic epistasis, RNA-seq/ChIP-seq/nucleosome mapping, co-IP and Hi-C across yeast and human studies\",\n      \"pmids\": [\"30681413\", \"31837996\", \"31365865\", \"31582854\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether cohesin and H2Bub effects share a common SPT16 surface unknown\", \"Direct vs indirect contribution to TAD formation not separated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Connected FACT to transcription-coupled DSB responses and DNA-structure sensing, with OTUD5-SPT16 driving Pol II arrest and SSRP1 recognizing Z-DNA-prone sequences to trigger p53.\",\n      \"evidence\": \"DUB RNAi screen, co-IP, RNA synthesis assays; in vitro DNA binding and curaxin ChIP with p53 readout\",\n      \"pmids\": [\"30508113\", \"28082391\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether SPT16 or SSRP1 is the primary structural sensor not resolved\", \"Physiological prevalence of Z-DNA sensing unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Established FACT as essential for surviving replication stress by maintaining MCM2-7 retention and enabling ATR/CHK1 checkpoint activation.\",\n      \"evidence\": \"Knockdown/knockout, chromatin fractionation, RPA imaging, checkpoint phospho-analysis, DNA fiber assay in mammalian cells\",\n      \"pmids\": [\"32533099\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs chromatin-mediated effect on MCM retention not distinguished\", \"Single-lab findings\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Visualized FACT acting during active Pol II transcription, showing it binds partially unraveled nucleosomes and excludes Chd1/Spt5 to position reassembly upstream.\",\n      \"evidence\": \"Cryo-EM of yeast Pol II-Spt4/5-nucleosome complexes and in vitro transcription reconstitution\",\n      \"pmids\": [\"33846633\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinetic coupling between Pol II passage and FACT reassembly not measured\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined domain-specific recruitment of FACT to the replication fork via SPT16 N-terminus-Tof1 interaction, and showed nucleosome reorganization requires the middle and C-terminal domains.\",\n      \"evidence\": \"Single-molecule FRET, structure-guided pulldowns, in vitro chromatin replication\",\n      \"pmids\": [\"35061899\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the analogous SPT16-fork interaction operates in human cells not shown here\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Linked FACT to metabolic and stress signaling, with PKM2-derived pyruvate binding SSRP1 to enhance γH2AX chromatin loading, and FACT acting downstream of TFEB/TFE3 to remodel stress-gene promoters.\",\n      \"evidence\": \"Co-IP, in vitro binding, γH2AX loading assays, phospho-mutant analysis; co-IP, knockdown/inhibitor, ChIP, RT-qPCR\",\n      \"pmids\": [\"35048565\", \"35230915\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct SPT16 contribution to these signaling interactions not isolated from SSRP1\", \"Single-lab studies\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated in vivo that FACT maintains chromatin architecture required for promoter-proximal Pol II pausing and productive elongation, anchoring the mechanism in human cells.\",\n      \"evidence\": \"Auxin-inducible rapid FACT depletion with PRO-seq, ChIP-seq, RNA-seq, ATAC/MNase-seq\",\n      \"pmids\": [\"38810649\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct mechanism linking +1 nucleosome maintenance to pause stability not fully resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How FACT's distinct activities — disassembly, reassembly, repressive locus-specific control, repair, and architectural roles — are selectively deployed and regulated at individual genomic sites in vivo remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model for context-dependent targeting\", \"Regulation distinguishing activating vs repressive FACT function unknown\", \"Structural basis of repair-specific partner interactions undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [0, 2, 3, 4]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [3, 14]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 5, 7, 26]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [12, 23]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [3, 5, 18, 26]},\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 5, 26]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [3, 4, 17, 20]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [10, 11, 19]},\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [9, 22, 24]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"complexes\": [\"FACT complex\"],\n    \"partners\": [\"SSRP1\", \"RNF20\", \"Nek9\", \"Tof1\", \"OTUD5\", \"Usp7\", \"PKM2\", \"TFEB\"],\n    \"other_free_text\": []\n  }\n}\n```","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}