{"gene":"TADA2A","run_date":"2026-04-28T21:42:58","timeline":{"discoveries":[{"year":1992,"finding":"ADA2 (yeast) was identified genetically as a transcriptional adaptor required for the activity of acidic activation domains (VP16, GCN4) but not for all activators (e.g., GAL4-HAP4). Mutations in ADA2 abolished transcriptional responses to GAL4-VP16 and GCN4 in cell-free extracts while leaving basal transcription intact, placing ADA2 as a selective coactivator bridging acidic activators and the general transcription machinery.","method":"Genetic selection for resistance to GAL4-VP16 toxicity in yeast; in vitro transcription assays with ada2 mutant extracts","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — foundational genetic screen plus in vitro transcription assays; highly cited, replicated by subsequent work","pmids":["1638630"],"is_preprint":false},{"year":1993,"finding":"ADA3 was identified as a second transcriptional adaptor with a phenotypic spectrum similar to ADA2 (reduced VP16/GCN4 activation, slow growth, temperature sensitivity). Double mutant ada2 ada3 strains showed no additive growth or transcriptional defects, establishing that ADA2 and ADA3 function in the same pathway.","method":"Genetic selection; ada2/ada3 double mutant epistasis analysis; in vitro transcription","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with clear double-mutant phenotype, replicated across multiple labs","pmids":["8413201"],"is_preprint":false},{"year":1994,"finding":"ADA2 (yeast) directly binds the VP16 acidic activation domain in vitro, and the amino-terminal region of ADA2 mediates this interaction. ADA2 fused to a heterologous DNA-binding domain activates transcription in vivo in an ADA3-dependent manner, consistent with ADA2 functioning as a physical bridge between activators and the basal machinery.","method":"In vitro binding assays (GST pulldown); LexA fusion transcriptional activation assays in yeast","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — direct binding assay plus functional activation assay; replicated in subsequent studies","pmids":["7972120"],"is_preprint":false},{"year":1994,"finding":"GCN5 and ADA2 (yeast) interact physically (co-immunoprecipitation in vitro and yeast two-hybrid in vivo) and function in the same complex or pathway (no additive effects in gcn5 ada2 double mutants). Both are required for VP16- and GCN4-dependent activation. The bromodomain of GCN5 is functionally important for transcriptional activation but not for ADA2 binding.","method":"Yeast two-hybrid assay; co-immunoprecipitation; gcn5 ada2 double-mutant epistasis analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP plus genetic epistasis; independently confirmed by multiple laboratories","pmids":["7957049"],"is_preprint":false},{"year":1995,"finding":"ADA2 (yeast) physically interacts with TBP (TATA-binding protein) but not TFIIB. In yeast nuclear extracts, the association of VP16 activation domain with TBP (but not TFIIB) is dependent on ADA2. The N-terminus of ADA2 directly binds VP16, while ADA2 also interacts with GCN4 activation domain but not HAP4. These physical interactions correlate with ADA2's functional selectivity in vivo.","method":"GST pulldown with recombinant proteins; co-immunoprecipitation from yeast nuclear extracts; domain mapping","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal binding assays (recombinant pulldown + nuclear extract co-IP) with domain mapping","pmids":["7642611"],"is_preprint":false},{"year":1995,"finding":"ADA2, ADA3, and GCN5 form a heterotrimeric complex in vitro, with ADA2 serving as the linchpin that holds ADA3 and GCN5 together. The C-terminal domain of ADA3 alone is sufficient for heterotrimeric complex formation in vitro and for ADA2-dependent activation in vivo. Activation by LexA-ADA3 fusions is regulated by ADA2 levels, and LexA-ADA2 fusion activation is regulated by ADA3 levels, indicating they form a complex in cells.","method":"In vitro complex reconstitution; LexA fusion transcriptional assays in yeast; ADA3 domain deletion analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution of trimeric complex with domain dissection, replicated across labs","pmids":["7862114"],"is_preprint":false},{"year":1995,"finding":"Genetic evidence confirms GCN5 and ADA2 interact and define one complex mediating transcriptional activation in yeast. LexA-GCN5 activates transcription only in the presence of wild-type ADA2 (and vice versa), and the bromodomain of GCN5 is required for this complex function. gcn5 ada2 double disruption shows no additive effects.","method":"Genetic epistasis (double disruption); LexA-fusion transcription activation assays in yeast","journal":"Molecular & general genetics : MGG","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis plus functional transcription assay; single lab but consistent with other studies","pmids":["7898440"],"is_preprint":false},{"year":1996,"finding":"Human ADA2 (hADA2, later designated hADA2α/TADA2A) was identified as a functional homolog of yeast ADA2. hADA2 interacts with hGCN5 in the yeast two-hybrid assay (and hGCN5 interacts with yADA2), contains a cryptic activation domain, and augments GAL4-VP16 activation in human HeLa cells. GAL4-hADA2 fusion activates transcription in HeLa cells, demonstrating functional conservation in human cells.","method":"Yeast two-hybrid assay; transient transfection in HeLa cells; sequence conservation analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — two-hybrid interaction plus functional transcription activation in human cells; foundational identification of human TADA2A","pmids":["8552087"],"is_preprint":false},{"year":1997,"finding":"In yeast, NGG1p/ADA3p and ADA2p are co-immunoprecipitated from whole-cell extracts, with <2% of ADA2p not associated with NGG1p, demonstrating near-complete association in vivo. Stability of each protein depends on the presence of the other. ADA2/ADA3-containing complexes exist in multiple sizes (>2 MDa, ~900 kDa, ~200 kDa) by ion-exchange and gel-filtration chromatography, and at least one complex associates with TBP via residues 274–307 of NGG1p/ADA3.","method":"Co-immunoprecipitation from yeast whole-cell extracts; ion-exchange and gel-filtration chromatography; stability assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP plus biochemical fractionation showing multiple native complexes","pmids":["9038164"],"is_preprint":false},{"year":1997,"finding":"GCN5 HAT activity is functionally linked to ADA2 interaction in vivo: the minimal catalytic HAT domain of GCN5 is necessary but not sufficient for full in vivo function — interaction with ADA2 is additionally required for complementation of growth and transcriptional activation in gcn5 mutant cells. LexA-GCN5 fusion activates transcription requiring both the HAT domain and the ADA2-interaction domain.","method":"Domain deletion mutagenesis of GCN5; complementation assays in gcn5 yeast; LexA-GCN5 transcription activation assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1–2 — mutagenesis combined with functional complementation and transcription assays","pmids":["9034338"],"is_preprint":false},{"year":1997,"finding":"ADA1 was identified as an additional component of the ADA/GCN5 complex (~2 MDa). ADA1 interacts with other ADA proteins as shown by partial purification and co-immunoprecipitation. ada1 mutants show broader transcriptional defects than ada2/ada3/gcn5 mutants, suggesting the ADA/GCN5 complex has two separable functional modules.","method":"Co-immunoprecipitation; partial biochemical purification; transcriptional reporter assays in yeast","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP plus functional genetic evidence; single lab","pmids":["9154821"],"is_preprint":false},{"year":1997,"finding":"TADA2A (human TADA2L/hADA2α) and GCN5L2 co-localize to chromosome 17q12–q21 by FISH and display similar tissue expression patterns across human tissues by Northern blot, suggesting coordinated regulation consistent with their functional interaction in a conserved complex.","method":"Fluorescence in situ hybridization (FISH); Northern blot analysis across human tissues","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 3 — localization and expression data; no direct functional assay of the human protein","pmids":["9073520"],"is_preprint":false},{"year":1997,"finding":"Human GCN5 exists in a stable macromolecular complex (~67 Å Stokes radius, large complex) in human K562 erythroleukemia cells, but human ADA2 is resolved as a monomer (~35 Å) by gel-filtration chromatography, suggesting that unlike in yeast, human GCN5 and ADA2 are not stably associated with each other in a constitutive complex in this cell type.","method":"Gel-filtration chromatography of human K562 cell extracts; HAT activity fractionation","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical fractionation in human cells; single lab, single method","pmids":["9398325"],"is_preprint":false},{"year":1998,"finding":"TADA2A (hADA2α) is a stable component of the human PCAF histone acetyltransferase complex, which contains more than 20 subunits including TAF subunits with histone fold motifs (hTAFII31, hTAFII20/15 — H3- and H2B-like). This establishes TADA2A as part of the human PCAF/SAGA-type coactivator complex.","method":"Affinity purification of the PCAF complex; mass spectrometry and peptide sequencing of subunits","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — affinity purification and mass spectrometry of native human complex; highly cited","pmids":["9674425"],"is_preprint":false},{"year":1999,"finding":"Within the native human PCAF complex containing TADA2A, PCAF acetylates primarily lysine 14 of histone H3 and less efficiently lysine 8 of H4 on mononucleosomal substrates, and the complex polypeptides (including TADA2A/ADA2α) do not alter the substrate specificity of PCAF.","method":"In vitro HAT assay with mononucleosomes; Edman degradation of acetylated histones to identify acetylation sites","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro enzymatic assay on nucleosomal substrate within native complex; single study","pmids":["9880483"],"is_preprint":false},{"year":2001,"finding":"Yeast Ada2 and Ada3 together with Gcn5 form the catalytic core of both the ADA and SAGA HAT complexes (the minimal module necessary and sufficient for nucleosomal HAT activity in vitro). Ada2 potentiates the Gcn5 catalytic activity; Ada3 facilitates nucleosomal acetylation and expanded lysine specificity. This catalytic core is necessary for nucleosomal HAT activity.","method":"Reconstitution of recombinant Ada2/Ada3/Gcn5 sub-complex; in vitro HAT assays on histones and nucleosomes; comparison with intact SAGA/ADA complexes","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution of catalytic module with nucleosomal HAT assays","pmids":["11773077"],"is_preprint":false},{"year":2002,"finding":"The SANT domain of Ada2 (yeast) is required for normal histone acetylation by the SAGA complex in vivo and in vitro. Deletion and substitution mutations within the SANT domain of Ada2 and specific regions of the Gcn5 HAT domain (distinct from the catalytic site) impair substrate (histone/nucleosome) recognition. This identifies the Ada2 SANT domain as a histone/nucleosome substrate recognition module within SAGA.","method":"Site-directed mutagenesis of Ada2 SANT domain and Gcn5 HAT domain; in vitro HAT assays; in vivo histone acetylation assays in yeast","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — mutagenesis combined with in vitro and in vivo HAT activity assays","pmids":["11777910"],"is_preprint":false},{"year":2003,"finding":"A novel human Ada2 homologue, hADA2β (distinct from hADA2α/TADA2A), was identified. hADA2β interacts selectively with the Gcn5-containing TFTC/STAGA complex but not stably with the PCAF complex (which contains hADA2α). hADA2β (but not ADA2α) also associates with human Swi/Snf via Baf57 interaction, and functions with Gcn5 (but not PCAF) or Brg1 to coactivate Pax5/BSAP-dependent transcription. This establishes TADA2A (hADA2α) as the specific ADA2 isoform in the PCAF complex.","method":"Yeast two-hybrid screen; in vitro co-immunoprecipitation; transient transfection coactivation assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal assays defining distinct complex membership of TADA2A vs. TADA2B","pmids":["12972612"],"is_preprint":false},{"year":2003,"finding":"In Drosophila, there are two Ada2 homologs (dAda2a and dAda2b) that reside in distinct GCN5-containing complexes. dAda2b is a component of dSAGA (~2 MDa), while dAda2a associates with dGcn5 in a smaller (~0.8 MDa) complex not incorporated into dSAGA. dAda2a-containing complexes concentrate at transcriptionally active regions on polytene chromosomes independently of dSAGA. Humans and mice also possess two Ada2 variants with high homology to dAda2a (→ TADA2A) and dAda2b (→ TADA2B), suggesting the mammalian homologs form two functionally distinct subgroups.","method":"Biochemical fractionation (glycerol gradient sedimentation, chromatography); immunoprecipitation; immunofluorescence on polytene chromosomes","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal biochemical and cell biological approaches; two independent Drosophila studies (PMIDs 12697829 and 12482983) reached the same conclusion","pmids":["12697829","12482983"],"is_preprint":false},{"year":2005,"finding":"In Drosophila, Ada2a (ortholog of human TADA2A) null mutants are late-larva lethal and show a distinct phenotype from Ada2b null mutants. Ada2a null mutation does not reduce histone H3 K14/K9 acetylation or TAF10 localization (unlike Ada2b null), indicating Ada2a and Ada2b have non-redundant, distinct functions. Ada2a null impairs cell proliferation and differentially affects specific gene expression (e.g., rosy gene) and Dmp53-mediated apoptosis.","method":"Loss-of-function Drosophila genetics (null alleles); phenotypic analysis; histone acetylation assays by western blot; TAF10 localization by immunostaining","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — clean null alleles with defined phenotypic readouts including histone modification levels","pmids":["16135810"],"is_preprint":false},{"year":2005,"finding":"The 5' boundary of ACACA lies within a CpG island harboring a bidirectional promoter shared with the divergently oriented TADA2L (TADA2A) gene. This shared promoter coregulates transcripts for TADA2L and ACACA asymmetrically across human and mouse tissues, with RNA Pol II concentration in the intergenic region reflecting transcript abundance in brain vs. liver. This defines the genomic context of TADA2A transcription regulation.","method":"5' RACE; genomic sequencing; RNA Pol II ChIP in mouse tissues; Northern blot","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 3 — ChIP and expression analysis of shared promoter; no direct functional assay of TADA2A protein","pmids":["15607423"],"is_preprint":false},{"year":2005,"finding":"Polyglutamine-expanded ataxin-7 is an integral subunit of the mammalian STAGA complex (which contains TADA2A/ADA2α). Poly(Q)-expanded ataxin-7 in STAGA dominantly inhibits GCN5-mediated nucleosomal histone acetylation in vitro and in SCA7 transgenic mice (by ChIP). TADA2A is thus a component of the human STAGA coactivator complex that can be functionally compromised in spinocerebellar ataxia type 7.","method":"Affinity purification of human STAGA; in vitro nucleosomal HAT assays; chromatin immunoprecipitation (ChIP) from SCA7 transgenic mouse retina","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 — native complex purification, in vitro HAT assay, and in vivo ChIP in transgenic mouse model","pmids":["15932940"],"is_preprint":false},{"year":2006,"finding":"In Drosophila, dAda2a (TADA2A ortholog) and dGcn5 genetically interact: loss of either causes similar chromosome structural defects and developmental abnormalities. In dAda2a mutants, nucleosomal H4 acetylation at K12 and K5 is significantly reduced while H3 K9/K14 acetylation (established by dAda2b-containing complexes) is unaffected. This establishes that the TADA2A-type Ada2 (dAda2a) directs Gcn5 toward H4 lysine acetylation specifically.","method":"Drosophila loss-of-function genetics; histone acetylation analysis by western blot (antibodies to H4K12ac, H4K5ac, H3K9ac, H3K14ac); chromosome squash analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — clean genetic analysis with specific histone modification readouts distinguishing two Ada2 paralogs","pmids":["17030603"],"is_preprint":false},{"year":2007,"finding":"Recombinant yeast Ada2/Ada3/Gcn5 sub-complex (the SAGA HAT module) was expressed and purified as a functional unit sufficient for acetylation of histones H3 and H2B on nucleosomes in vitro. BL21-CodonPlus E. coli strain enhanced purity of the metal-affinity-purified Ada2/Ada3/Gcn5 complex. This reconstituted complex serves as the minimal functional HAT module.","method":"Recombinant protein expression and purification; in vitro nucleosomal HAT assays","journal":"Methods (San Diego, Calif.)","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro reconstitution of minimal HAT module with nucleosomal substrate; methods paper","pmids":["17309836"],"is_preprint":false},{"year":2007,"finding":"GCN5 and PCAF (both associated with TADA2A/ADA2α vs. ADA2β isoforms respectively in distinct complexes) function as co-activators in at least two types of human multiprotein complexes: STAGA-type (~2 MDa) and ATAC-type (~700 kDa). These complexes possess both global histone acetylation activity and gene-specific coactivator functions.","method":"Biochemical purification; mass spectrometry; HAT activity assays","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — review integrating biochemical purification data from multiple studies; TADA2A identity in these complexes established","pmids":["17694077"],"is_preprint":false},{"year":2008,"finding":"Human ATAC (Ada Two-A containing) complex was purified and characterized; it contains ADA2-A (TADA2A), ADA3, STAF36, WDR5, POLE3/CHRAC17, POLE4, TAK1/MAP3K7, MBIP, and a novel YEATS2–NC2β histone fold module that interacts with TBP and negatively regulates transcription. TADA2A is thus a defining subunit of the human ATAC complex distinct from STAGA.","method":"Affinity purification of human ATAC complex from HeLa cells; mass spectrometry identification of subunits; TBP interaction assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — native complex purification and mass spectrometry; defines TADA2A as core ATAC subunit","pmids":["18838386"],"is_preprint":false},{"year":2008,"finding":"A conserved ~120-amino-acid central region of yeast Ada2 (the 'RLR' region) is required for normal Gcn5 HAT activity. The ada2-RLR allele (R211S, L212A, R215A) reduces Gcn5-mediated histone acetylation in vitro to ~40% of wild-type and nearly eliminates in vivo acetylation of H2B K16, while reducing H3 K9/K18 acetylation to ~40%. This region also binds phospholipids (phosphatidylserine), suggesting a possible regulatory interaction.","method":"Site-directed mutagenesis; in vitro HAT assays; in vivo chromatin histone acetylation at Ada2-regulated promoters; microarray expression analysis; phospholipid binding assay","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 1–2 — mutagenesis combined with in vitro and in vivo histone acetylation assays","pmids":["18950642"],"is_preprint":false},{"year":2009,"finding":"Ada2 (yeast) has a novel function in transcriptional silencing at telomeres and ribosomal DNA, distinct from its role in Gcn5-mediated activation. Ada2 binds telomeric chromatin and the silencing protein Sir2 in vivo (ChIP). Loss of ADA2 causes spreading of Sir2 and Sir3 into subtelomeric regions and decreased histone H4 K16 acetylation. Upon nutritional changes, Ada2 occupancy increases at subtelomeric regions adjacent to SAGA-inducible genes, derepressing silenced reporters.","method":"Chromatin immunoprecipitation (ChIP) for Ada2, Sir2, Sir3 at telomeres and rDNA; in vivo silencing assays (telomeric reporter); histone modification analysis","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP with functional silencing assays; single lab","pmids":["19737915"],"is_preprint":false},{"year":2017,"finding":"Ada2 and Spt20 undergo co-translational assembly in yeast, dependent on the Ccr4-Not complex subunit Not5. SAGA mRNAs encoding a core set of subunits (including Ada2) are tethered together for co-translational assembly. Disruption of this co-translational assembly (via not5 deletion) impairs SAGA integrity, reducing histone acetylation.","method":"mRNA co-immunoprecipitation; polysome profiling; SAGA complex integrity assays; histone acetylation assays in yeast not5 mutants","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 — mRNA-protein association assays plus functional complex integrity readout; single lab","pmids":["28180299"],"is_preprint":false},{"year":2017,"finding":"Ada2(Gcn5)-dependent histone H3K14 acetylation (along with Sas3) is required for transcription elongation at the de-repressed FLO1 gene in yeast. In the absence of H3K14 acetylation, Swi/Snf recruitment and histone eviction proceed but RNAP II is absent from the coding region, demonstrating that Ada2-dependent H3 acetylation is required specifically for the transition from initiation to elongation.","method":"Chromatin immunoprecipitation (ChIP) for RNAP II, Swi/Snf, histone modifications; transcription kinetics assays in histone mutant and ada2 yeast strains","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP-based mechanistic dissection of elongation vs. initiation; single lab","pmids":["28115623"],"is_preprint":false},{"year":2018,"finding":"Crystal structures of a yeast Ada2/Gcn5 complex were determined using Fab antibody crystallization chaperones. Structural and biochemical analysis revealed that the Ada2 SANT domain activates Gcn5 HAT activity not by directly affecting histone peptide binding as previously proposed, but by enhancing Gcn5 binding to the enzymatic co-substrate acetyl-CoA. This suggests a mechanism for regulating chromatin modification enzyme activity by controlling co-substrate rather than substrate binding.","method":"X-ray crystallography of Ada2/Gcn5 complex; in vitro HAT activity assays; acetyl-CoA binding assays; mutagenesis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — crystal structure combined with biochemical activity and binding assays and mutagenesis","pmids":["30224453"],"is_preprint":false},{"year":2005,"finding":"Large-scale yeast two-hybrid screening of human proteins detected protein-protein interactions involving TADA2A (TADA2L), placing it in the human binary interactome network and identifying novel interaction partners consistent with its role in coactivator complexes.","method":"High-throughput yeast two-hybrid assay (CCSB-HI1 dataset); co-affinity purification validation","journal":"Nature","confidence":"Low","confidence_rationale":"Tier 3 — high-throughput screen; TADA2A interactions not individually validated","pmids":["16189514"],"is_preprint":false},{"year":2020,"finding":"The Ada2/Ada3/Gcn5/Sgf29 HAT module of SAGA is the minimal unit for Gcn5-mediated histone H3 acetylation at multiple positions. Structural and biochemical studies demonstrate that Ada2 activates Gcn5's intrinsically weak HAT activity, Ada3 facilitates nucleosomal acetylation and expanded lysine specificity, and Sgf29 binds H3K4me3 to recruit the module to active gene promoters. Two Ada2 isoforms (TADA2A and TADA2B) define distinct SAGA-related complexes with different histone substrate preferences.","method":"Review integrating structural studies, reconstitution biochemistry, and genetic data from multiple laboratories","journal":"Biochimica et biophysica acta. Gene regulatory mechanisms","confidence":"High","confidence_rationale":"Tier 1 — review synthesizing multiple independent structural, biochemical, and genetic studies","pmids":["32890768"],"is_preprint":false}],"current_model":"TADA2A (human ADA2α) is a transcriptional adaptor and core subunit of the PCAF/STAGA and ATAC histone acetyltransferase complexes, where it bridges acidic activation domains (VP16, GCN4) with TBP and potentiates GCN5/PCAF catalytic activity by enhancing acetyl-CoA binding via its SANT domain, enabling nucleosomal histone H3/H4 acetylation and transcription elongation; it is distinct from the paralogous TADA2B (ADA2β), which resides in SAGA-type complexes and directs H3K9/K14 acetylation, whereas TADA2A-containing complexes (ATAC) preferentially direct H4K5/K12 acetylation."},"narrative":{"teleology":[{"year":1992,"claim":"Establishing that a dedicated coactivator exists between acidic activators and the basal transcription machinery: yeast ADA2 was identified as a selective transcriptional adaptor required for VP16/GCN4-dependent activation but dispensable for basal transcription, founding the concept of activation-domain-specific coactivators.","evidence":"Genetic selection for GAL4-VP16 toxicity resistance in yeast; in vitro transcription with ada2 mutant extracts","pmids":["1638630"],"confidence":"High","gaps":["Mechanism of selectivity for acidic vs. other activation domains unknown","No biochemical identity of the complex or direct interactors","Mammalian relevance unaddressed"]},{"year":1994,"claim":"Defining ADA2 as a physical scaffold linking activators to the HAT enzyme GCN5: ADA2 directly binds the VP16 activation domain and physically interacts with GCN5, with epistasis showing they function in the same pathway, establishing the adaptor-HAT connection.","evidence":"GST pulldown binding assays; yeast two-hybrid; co-immunoprecipitation; gcn5/ada2 double-mutant epistasis","pmids":["7972120","7957049"],"confidence":"High","gaps":["Stoichiometry and full composition of native complex unknown","Whether ADA2 contacts TBP directly not yet tested"]},{"year":1995,"claim":"Resolving the trimeric core and dual bridging function: ADA2 forms a heterotrimeric complex with ADA3 and GCN5 (ADA2 as linchpin), and ADA2 also directly contacts TBP, establishing it as a bidirectional bridge between activator–HAT and the basal machinery.","evidence":"In vitro reconstitution of Ada2/Ada3/Gcn5 trimer; GST pulldown and co-IP for ADA2–TBP interaction; domain mapping","pmids":["7862114","7642611"],"confidence":"High","gaps":["Native complex size and additional subunits unknown","Whether ADA2–TBP interaction is direct in the context of a larger complex"]},{"year":1996,"claim":"Demonstrating evolutionary conservation in humans: human ADA2α (TADA2A) was cloned and shown to interact with hGCN5 and augment VP16-dependent activation in HeLa cells, establishing functional conservation from yeast to mammals.","evidence":"Yeast two-hybrid for hADA2–hGCN5 interaction; transient transfection transcription assays in HeLa cells","pmids":["8552087"],"confidence":"High","gaps":["Identity of the native human complex containing TADA2A unknown","Whether mammalian ADA2α is stably complexed with GCN5 in vivo unresolved"]},{"year":1998,"claim":"Placing TADA2A in a defined macromolecular coactivator complex: TADA2A was identified as a stable subunit of the human PCAF HAT complex (~20 subunits including TAF-like histone fold proteins), defining its physiological context.","evidence":"Affinity purification of native PCAF complex from human cells; mass spectrometry subunit identification","pmids":["9674425"],"confidence":"High","gaps":["Whether TADA2A also exists in non-PCAF complexes in human cells","Functional role of TADA2A within the PCAF complex not biochemically dissected"]},{"year":2001,"claim":"Identifying Ada2 as essential for nucleosomal HAT activity: reconstitution showed Ada2/Ada3/Gcn5 is the minimal catalytic HAT module sufficient for nucleosomal acetylation, with Ada2 potentiating Gcn5 catalytic activity.","evidence":"Recombinant sub-complex reconstitution; in vitro HAT assays on nucleosomal substrates","pmids":["11773077"],"confidence":"High","gaps":["Mechanism by which Ada2 potentiates Gcn5 activity unresolved at atomic level","Whether this applies to mammalian TADA2A–GCN5 not directly tested"]},{"year":2002,"claim":"Identifying the SANT domain as the functional element: mutations in the Ada2 SANT domain impaired histone acetylation in vitro and in vivo, establishing this domain as a histone/nucleosome recognition element within the HAT module.","evidence":"Site-directed mutagenesis of Ada2 SANT domain; in vitro and in vivo HAT assays in yeast","pmids":["11777910"],"confidence":"High","gaps":["Whether the SANT domain contacts histones directly or acts allosterically on Gcn5 unclear","Structural basis of SANT domain function not determined"]},{"year":2003,"claim":"Establishing paralog-specific complex membership: identification of TADA2B (hADA2β) demonstrated that TADA2A resides selectively in PCAF-type complexes while TADA2B resides in STAGA/TFTC-type complexes, with non-overlapping functions in coactivation.","evidence":"Yeast two-hybrid; co-immunoprecipitation; transient transfection coactivation assays in mammalian cells; Drosophila biochemical fractionation","pmids":["12972612","12697829"],"confidence":"High","gaps":["Whether TADA2A and TADA2B have distinct histone substrate specificities in mammalian cells","Structural basis for paralog-specific complex incorporation unknown"]},{"year":2006,"claim":"Resolving histone substrate specificity: Drosophila Ada2a (TADA2A ortholog) null mutants showed selective loss of H4 K5/K12 acetylation while H3 K9/K14 acetylation was unaffected, demonstrating that the TADA2A-type adaptor directs the HAT toward H4 lysines specifically.","evidence":"Drosophila null alleles; histone modification-specific western blots; chromosome structural analysis","pmids":["17030603"],"confidence":"High","gaps":["Whether this substrate specificity is conserved in mammalian TADA2A-containing complexes","Structural mechanism by which Ada2a redirects Gcn5 to H4 unknown"]},{"year":2008,"claim":"Defining the ATAC complex: human ATAC was purified and shown to contain TADA2A as a defining subunit alongside ADA3, WDR5, YEATS2, and other components, establishing ATAC as a distinct TADA2A-specific complex separate from STAGA.","evidence":"Affinity purification from HeLa cells; mass spectrometry; TBP interaction assays","pmids":["18838386"],"confidence":"High","gaps":["Genomic targets and biological functions of ATAC vs. STAGA in human cells not dissected","Regulation of ATAC assembly and recruitment unknown"]},{"year":2018,"claim":"Revealing the structural mechanism of Ada2-mediated HAT activation: crystal structures of Ada2/Gcn5 showed that the Ada2 SANT domain enhances Gcn5 activity by promoting acetyl-CoA co-substrate binding rather than by improving histone substrate recognition, revising the prior model.","evidence":"X-ray crystallography of Ada2/Gcn5 complex; acetyl-CoA binding assays; mutagenesis and in vitro HAT assays","pmids":["30224453"],"confidence":"High","gaps":["Structure of full Ada2/Ada3/Gcn5 HAT module on nucleosomal substrate not yet determined","Whether acetyl-CoA sensing by Ada2 constitutes a metabolic regulatory mechanism in vivo"]},{"year":null,"claim":"The genomic targets and functional consequences of TADA2A-containing ATAC complex activity in mammalian cells, and whether TADA2A loss-of-function causes human disease, remain to be established through direct human genetic and functional genomic studies.","evidence":"","pmids":[],"confidence":"Low","gaps":["No human genetic disease directly linked to TADA2A mutations in the literature","Genome-wide binding and acetylation targets of human ATAC complex not mapped","Role of TADA2A in mammalian development and tissue-specific gene regulation unexplored"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,2,7,9,15]},{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[16,30,32]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[2,4,5]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[8,13,18,27]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[18,22,27]}],"pathway":[{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[15,16,22,30,32]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,7,9,29]}],"complexes":["PCAF complex","STAGA complex","ATAC complex","Ada2/Ada3/Gcn5 HAT module"],"partners":["GCN5","PCAF","ADA3","YEATS2","WDR5","TBP","SGF29","ATXN7"],"other_free_text":[]},"mechanistic_narrative":"TADA2A is a transcriptional adaptor protein that serves as a core scaffolding subunit of the PCAF, STAGA, and ATAC histone acetyltransferase complexes, where it bridges acidic activation domains of transcription factors (VP16, GCN4) with TBP and potentiates GCN5/PCAF-mediated histone acetylation [PMID:1638630, PMID:7642611, PMID:9674425, PMID:18838386]. Within the catalytic HAT module formed by Ada2/Ada3/Gcn5, TADA2A activates the intrinsically weak acetyltransferase activity of GCN5 through its SANT domain, which enhances acetyl-CoA co-substrate binding rather than histone substrate recognition [PMID:30224453, PMID:11773077]. TADA2A-containing complexes (ATAC) preferentially direct histone H4 K5/K12 acetylation, distinguishing them from the paralogous TADA2B-containing SAGA-type complexes that target H3 K9/K14, and this Ada2-dependent acetylation is required for the transition from transcription initiation to elongation [PMID:17030603, PMID:28115623]. Polyglutamine-expanded ataxin-7 incorporated into TADA2A-containing STAGA dominantly inhibits nucleosomal histone acetylation, linking TADA2A complex dysfunction to spinocerebellar ataxia type 7 [PMID:15932940]."},"prefetch_data":{"uniprot":{"accession":"O75478","full_name":"Transcriptional adapter 2-alpha","aliases":["Transcriptional adapter 2-like","ADA2-like protein"],"length_aa":443,"mass_kda":51.5,"function":"Component of the ATAC complex, a complex with histone acetyltransferase activity on histones H3 and H4. Required for the function of some acidic activation domains, which activate transcription from a distant site (By similarity). Binds double-stranded DNA. Binds dinucleosomes, probably at the linker region between neighboring nucleosomes. Plays a role in chromatin remodeling. May promote TP53/p53 'Lys-321' acetylation, leading to reduced TP53 stability and transcriptional activity (PubMed:22644376). 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CCDC101","url":"https://www.omim.org/entry/613374"},{"mim_id":"613373","title":"YEATS DOMAIN-CONTAINING PROTEIN 2; YEATS2","url":"https://www.omim.org/entry/613373"},{"mim_id":"609431","title":"MAP3K12-BINDING INHIBITORY PROTEIN; MBIP","url":"https://www.omim.org/entry/609431"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nuclear speckles","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":58695,"output_tokens":9097,"usd":0.15627},"round2_rules_fired":"R2","round2_stage2":{"model":"claude-opus-4-6","input_tokens":12598,"output_tokens":3079,"usd":0.209948}},"stage1_raw":"Looking at the corpus, I need to distinguish between two very different genes sharing related symbols:\n\n1. **TADA2A** (human/mammalian) — a transcriptional adaptor/coactivator subunit of SAGA/ADA complexes, interacting with GCN5/KAT2A\n2. **ADA2** (human CECR1 gene product) — adenosine deaminase 2, an extracellular enzyme involved in vasculopathy/DADA2 disease\n\nThe query gene is **TADA2A** (Transcriptional Adaptor 2A), which is the human homolog of yeast Ada2, a component of SAGA/HAT complexes. Papers about CECR1/adenosine deaminase 2 (the vasculopathy gene) are symbol collisions for this query and should be excluded.\n\nI will include yeast Ada2 and Drosophila Ada2a/Ada2b papers as orthologs since their function is consistent with mammalian TADA2A.\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1992,\n      \"finding\": \"Yeast ADA2 was identified as a transcriptional adaptor required for the activity of acidic activation domains (VP16, GCN4) but not for all activators (e.g., HAP4); ada2 mutant extracts showed normal basal transcription but failed to respond to GAL4-VP16 or GCN4, establishing ADA2 as a selective coactivator bridging activators and general transcription factors.\",\n      \"method\": \"Genetic selection (GAL4-VP16 toxicity screen), in vitro transcription assays with mutant yeast extracts, gene disruption\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — foundational genetic and biochemical study, replicated extensively across labs\",\n      \"pmids\": [\"1638630\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Yeast ADA2 physically binds the VP16 acidic activation domain (but not HAP4) and, when fused to a heterologous DNA-binding domain, activates transcription in vivo via ADA3; the amino terminus of ADA2 mediates interaction with VP16.\",\n      \"method\": \"GST pulldown/binding assay with activation domain peptides, LexA-ADA2 fusion transcriptional activation assay, genetic epistasis with ada3 mutants\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct protein-protein binding assay plus in vivo functional validation, replicated\",\n      \"pmids\": [\"7972120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"GCN5 binds ADA2 both by yeast two-hybrid assay in vivo and by co-immunoprecipitation in vitro; double mutant analysis shows GCN5 and ADA2 function together in the same complex or pathway; the bromodomain of GCN5 is not required for ADA2 interaction.\",\n      \"method\": \"Yeast two-hybrid assay, co-immunoprecipitation, double-mutant genetic analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus genetic epistasis, replicated across labs\",\n      \"pmids\": [\"7957049\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"ADA2 directly interacts with TBP (TATA-binding protein) in yeast nuclear extracts, and this TBP/VP16 association is ADA2-dependent; ADA2 also directly binds VP16 and GCN4 activation domains but not HAP4; the N-terminus of ADA2 provides the determinants for interaction with activation domains.\",\n      \"method\": \"Co-immunoprecipitation from yeast nuclear extracts, direct binding assays with recombinant proteins, domain mapping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple binding assays with domain mapping, consistent with prior genetic data\",\n      \"pmids\": [\"7642611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"ADA2, ADA3, and GCN5 form a heterotrimeric complex in vitro with ADA2 as the central linchpin holding ADA3 and GCN5 together; ADA3 has two separable functional domains, with the C-terminal domain sufficient for trimeric complex formation.\",\n      \"method\": \"In vitro reconstitution of trimeric complex, co-immunoprecipitation, LexA fusion transcriptional assays, ADA3 domain deletion analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of trimeric complex with domain mapping, foundational study\",\n      \"pmids\": [\"7862114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Human ADA2 (hADA2/TADA2A) is a functional homolog of yeast ADA2: it interacts with human GCN5 (hGCN5) in yeast two-hybrid assays (and hGCN5 cross-interacts with yADA2), GAL4-hADA2 activates transcription in HeLa cells, and hADA2 or hGCN5 augment GAL4-VP16 activation in human cells.\",\n      \"method\": \"Yeast two-hybrid assay, transient transfection transcriptional activation assay in HeLa cells, yeast complementation\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional conservation established by multiple orthogonal assays in human cells\",\n      \"pmids\": [\"8552087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Yeast NGG1p/ADA3p and ADA2p are co-immunoprecipitated from whole-cell extracts; less than 2% of cellular ADA2p exists outside the NGG1p complex; stability of each protein depends on the other; ADA2/ADA3-containing complexes associate with TBP, and this requires residues 274–307 of NGG1p.\",\n      \"method\": \"Co-immunoprecipitation from yeast whole-cell extracts, ion-exchange and gel-filtration chromatography, stability assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with multiple chromatographic approaches, mutant domain mapping\",\n      \"pmids\": [\"9038164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"GCN5 HAT activity and GCN5-ADA2 interaction are both required for full in vivo function; the minimal HAT catalytic domain of GCN5 is necessary but not sufficient — the ADA2-interaction domain is also required for complementation of gcn5 mutant growth and transcriptional activation; the bromodomain is dispensable for HAT activity but needed for full complementation.\",\n      \"method\": \"Deletion/substitution mutagenesis of GCN5 domains, in vivo complementation of gcn5 mutants, LexA-GCN5 fusion transcriptional assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — systematic mutagenesis with functional in vivo readouts, seminal study\",\n      \"pmids\": [\"9034338\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Human GCN5 exists in a large macromolecular complex (~67 Å Stokes radius) in K562 cells, but human ADA2 (~35 Å, consistent with monomer) is not stably associated with human GCN5 under these conditions, contrasting with the stable yeast GCN5-Ada2 complex.\",\n      \"method\": \"Gel-filtration chromatography of human K562 nuclear extracts, HAT activity fractionation\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — single lab biochemical fractionation, notable but not replicated\",\n      \"pmids\": [\"9398325\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Human TADA2A (TADA2L) and GCN5L2 co-localize to chromosome 17q12-q21 and are co-expressed at similar levels across all human tissues examined, suggesting coordinated regulation.\",\n      \"method\": \"FISH chromosomal mapping, Northern blot tissue expression analysis\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — expression/localization data without direct functional mechanistic link\",\n      \"pmids\": [\"9073520\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Yeast Ada2, Ada3, and Gcn5 form a catalytic core (HAT module) of ADA and SAGA complexes that is necessary and sufficient for nucleosomal HAT activity in vitro; Ada2 potentiates Gcn5 catalytic activity; Ada3 facilitates nucleosomal acetylation and expanded lysine specificity.\",\n      \"method\": \"Reconstitution of Ada2/Ada3/Gcn5 subcomplex, in vitro HAT assay on nucleosomes, genetic deletion analysis in yeast extracts\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with nucleosomal substrate, genetic validation\",\n      \"pmids\": [\"11773077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The SANT domain of yeast Ada2 is required for normal histone acetylation by SAGA; SANT domain deletions/substitutions reduce Gcn5-mediated acetylation of nucleosomal substrates, and this domain functions in histone/nucleosome substrate recognition rather than in Gcn5 catalysis per se.\",\n      \"method\": \"SANT domain deletion and substitution mutagenesis, in vitro HAT assays with nucleosomal substrates, in vivo acetylation analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis plus in vitro and in vivo HAT assays\",\n      \"pmids\": [\"11777910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Drosophila has two Ada2 homologs (dAda2a and dAda2b): only dAda2b is incorporated into SAGA-type complexes; dAda2a associates with dGcn5 in a distinct, smaller (~0.8 MDa) complex that is not SAGA and is concentrated at transcriptionally active polytene chromosome regions; humans and mice also have two Ada2 variants homologous to dAda2a and dAda2b respectively.\",\n      \"method\": \"Biochemical fractionation (glycerol gradient, chromatography), co-immunoprecipitation, immunolocalization on polytene chromosomes, yeast two-hybrid\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal biochemical and cell biological approaches, replicated by independent lab (PMID:12482983)\",\n      \"pmids\": [\"12697829\", \"12482983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Human Ada2beta (TADA2B isoform) — distinct from previously characterized hAda2alpha (TADA2A) — selectively associates with the Gcn5-containing TFTC/STAGA complex (not PCAF complex); TADA2A (Ada2alpha) is a stable component of the human PCAF acetyltransferase complex; Ada2beta (but not Ada2alpha) also interacts with Baf57 and human SWI/SNF, and co-activates Pax5 with Gcn5 or Brg1.\",\n      \"method\": \"Co-immunoprecipitation, yeast two-hybrid, in vitro binding assay, transient transfection transcriptional assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple binding and functional assays establishing distinct biochemical identity of two human Ada2 paralogs\",\n      \"pmids\": [\"12972612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"TADA2A (TADA2L) gene shares a bidirectional CpG-island promoter with the divergently oriented ACACA gene; this promoter co-regulates both transcripts asymmetrically across human and mouse tissues, with higher RNA Pol II density in brain than liver.\",\n      \"method\": \"5' RACE, genomic sequencing, RNA Pol II ChIP, Northern blot across tissues in human/mouse/rat/ovine\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — identifies regulatory genomic architecture but no direct mechanistic functional assay of TADA2A protein\",\n      \"pmids\": [\"15607423\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Drosophila Ada2a and Ada2b null mutants are each lethal at different developmental stages (late larva vs. late pupa); Ada2b loss reduces histone H3 K14 and K9 acetylation and alters TAF10 localization, while Ada2a loss does not affect H3 acetylation; the two Ada2 homologs cannot substitute for each other, demonstrating functionally distinct roles.\",\n      \"method\": \"Null mutant generation, genetic complementation with transgenes, histone acetylation immunostaining, TAF10 localization by immunofluorescence, pole-cell transplantation\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean null mutants with multiple orthogonal phenotypic readouts\",\n      \"pmids\": [\"16135810\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Loss of Drosophila dAda2a function results in significant reduction of nucleosomal H4 acetylation at lysines 12 and 5, while H3 K9/K14 acetylation (established by dAda2b-containing complexes) is unaffected; dGcn5 and dAda2a genetically interact and are required for the same chromosome structural and developmental processes.\",\n      \"method\": \"Ada2a mutant analysis, histone acetylation immunostaining with site-specific antibodies, genetic interaction analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean mutant with site-specific histone acetylation readouts, distinguishes Ada2a from Ada2b function\",\n      \"pmids\": [\"17030603\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Recombinant yeast Ada2/Ada3/Gcn5 subcomplex can be expressed and purified as a minimal module sufficient for HAT activity on nucleosomal substrates (acetylating histones H3 and H2B).\",\n      \"method\": \"Recombinant protein expression and purification, in vitro nucleosomal HAT assay\",\n      \"journal\": \"Methods (San Diego, Calif.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with nucleosomal substrates\",\n      \"pmids\": [\"17309836\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"A conserved ~120-aa central region of yeast Ada2 (residues including R211, L212, R215) regulates Gcn5 HAT activity; ada2-RLR mutation reduces Gcn5-mediated histone acetylation in vitro to ~40% of wild-type and nearly abolishes H2B K16 acetylation at Ada2-regulated promoters in vivo; this central region of Ada2 also binds phospholipids, with phosphatidylserine binding correlating with Ada2 function.\",\n      \"method\": \"Clustered alanine mutagenesis, in vitro HAT assays, chromatin immunoprecipitation of acetylation marks, microarray gene expression, phospholipid binding assay\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis combined with in vitro and in vivo acetylation assays and genome-wide expression analysis\",\n      \"pmids\": [\"18950642\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Yeast Ada2 promotes transcriptional silencing at telomeres and ribosomal DNA (a novel function distinct from Gcn5 coactivation); Ada2 binds telomeric chromatin and Sir2 in vivo; loss of ADA2 causes spreading of Sir2 and Sir3 into subtelomeric regions and decreased histone H4 K16 acetylation; this boundary activity is mechanistically distinct from that of Sas2.\",\n      \"method\": \"Chromatin immunoprecipitation of Ada2 at telomeres, Co-IP with Sir2, silencing reporter assays, histone acetylation analysis, genetic comparison with sas2 mutants\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches establishing novel silencing boundary function\",\n      \"pmids\": [\"19737915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SAGA complex mRNAs encoding a core set of subunits including Ada2 are tethered together for co-translational assembly; the Ccr4-Not complex subunit Not5 binds SAGA mRNAs and promotes co-translational assembly of Ada2 and Spt20, which is required for SAGA integrity.\",\n      \"method\": \"mRNA co-purification with SAGA subunits, Not5 binding to SAGA mRNAs, genetic analysis of not5 mutants on SAGA integrity\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — novel co-translational assembly mechanism, single lab study\",\n      \"pmids\": [\"28180299\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Crystal structures of yeast Ada2/Gcn5 complex (using Fab chaperones) reveal that the Ada2 SANT domain activates Gcn5 HAT activity not by affecting histone peptide binding, but by enhancing Gcn5 binding of the enzymatic cosubstrate acetyl-CoA.\",\n      \"method\": \"Crystal structure determination using Fab crystallization chaperones, biochemical acetyl-CoA binding assays, histone peptide binding assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional biochemical validation, mechanistically definitive\",\n      \"pmids\": [\"30224453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The Ada2/Ada3/Gcn5/Sgf29 HAT module of SAGA has been structurally and biochemically characterized: Ada2 (via its SANT domain) enhances Gcn5 acetyl-CoA binding to activate HAT activity; Ada3 facilitates nucleosomal acetylation; Sgf29 reads histone H3K4 methylation; Ada2 isoforms (corresponding to TADA2A and TADA2B) define distinct SAGA-related complexes with different substrate specificities.\",\n      \"method\": \"Review synthesizing crystal structures, biochemical reconstitution, mutagenesis, and histone modification crosstalk studies\",\n      \"journal\": \"Biochimica et biophysica acta. Gene regulatory mechanisms\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — review of multiple Tier 1 structural and biochemical studies, well-established mechanism\",\n      \"pmids\": [\"32890768\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TADA2A is a transcriptional adaptor/coactivator subunit of the SAGA and ADA histone acetyltransferase complexes that acts as the central scaffold bridging GCN5 (KAT2A) and ADA3 in the HAT module; its SANT domain directly enhances GCN5 binding to the cosubstrate acetyl-CoA (rather than to histone substrate) to stimulate H3/H2B nucleosomal acetylation, while its N-terminus mediates interaction with acidic transcriptional activation domains and TBP to connect promoter-bound activators to the general transcription machinery; in mammals, two Ada2 paralogs (TADA2A and TADA2B) define biochemically and functionally distinct GCN5-containing complexes (PCAF complex vs. TFTC/STAGA), with TADA2A being a stable component of the PCAF acetyltransferase complex.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper first, then extract discoveries only from KEPT papers.\n\n**Classification:**\n\nPapers about TADA2A (transcriptional adaptor 2A, the canonical coactivator protein in SAGA/ADA complexes):\n- KEEP: Papers [2],[3],[4],[5],[7],[8],[9],[13],[15],[16],[17],[19],[21],[22],[23],[25],[29],[30],[32],[39],[40],[41],[49],[51],[52],[62],[71],[73] from retrieved corpus\n- KEEP from gene2pubmed: [13],[18],[19],[20],[27],[28],[30]\n\n**EXCLUDE - Alias collision (ADA2 = adenosine deaminase 2 / CECR1):**\nPapers [1],[6],[10],[11],[12],[18],[20],[24],[26],[27],[28],[33],[35],[37],[43],[45],[46],[47],[48],[50],[53],[55],[57],[58],[60],[63],[64],[65],[66],[68],[69],[70],[72],[74],[75],[76],[77],[78],[79],[82],[83],[85],[86],[87],[88],[89],[90],[91],[92] (retrieved) — these are about adenosine deaminase 2 (CECR1/ADA2), not the transcriptional adaptor TADA2A.\n\n**EXCLUDE - Symbol collision (plant/non-ortholog):**\nPapers [14],[34],[44],[54],[59],[98] — Arabidopsis ADA2/rice ADA2 with plant-specific functions incompatible with mammalian gene context.\n\n**EXCLUDE - Alt-locus products (circRNA):**\nPapers [31],[61] — circTADA2A, not the canonical protein.\n\n**EXCLUDE - Fungal/parasitic organisms not orthologous:**\nPapers [36],[38],[42],[56],[81],[84] — Toxoplasma, Candida, Plasmodium, Beauveria.\n\n**EXCLUDE - Pure expression/genomic/clinical papers with no mechanistic data:**\nPapers [27 (retrieved, HIV ADA enzyme)], [67],[93],[94],[95],[96],[97],[99],[100] and gene2pubmed papers [1],[2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[14],[15],[16],[17],[21],[22],[23],[24],[25],[26],[29].\n\nNow extracting from KEPT papers:\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1992,\n      \"finding\": \"ADA2 (yeast) was identified genetically as a transcriptional adaptor required for the activity of acidic activation domains (VP16, GCN4) but not for all activators (e.g., GAL4-HAP4). Mutations in ADA2 abolished transcriptional responses to GAL4-VP16 and GCN4 in cell-free extracts while leaving basal transcription intact, placing ADA2 as a selective coactivator bridging acidic activators and the general transcription machinery.\",\n      \"method\": \"Genetic selection for resistance to GAL4-VP16 toxicity in yeast; in vitro transcription assays with ada2 mutant extracts\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — foundational genetic screen plus in vitro transcription assays; highly cited, replicated by subsequent work\",\n      \"pmids\": [\"1638630\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"ADA3 was identified as a second transcriptional adaptor with a phenotypic spectrum similar to ADA2 (reduced VP16/GCN4 activation, slow growth, temperature sensitivity). Double mutant ada2 ada3 strains showed no additive growth or transcriptional defects, establishing that ADA2 and ADA3 function in the same pathway.\",\n      \"method\": \"Genetic selection; ada2/ada3 double mutant epistasis analysis; in vitro transcription\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with clear double-mutant phenotype, replicated across multiple labs\",\n      \"pmids\": [\"8413201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"ADA2 (yeast) directly binds the VP16 acidic activation domain in vitro, and the amino-terminal region of ADA2 mediates this interaction. ADA2 fused to a heterologous DNA-binding domain activates transcription in vivo in an ADA3-dependent manner, consistent with ADA2 functioning as a physical bridge between activators and the basal machinery.\",\n      \"method\": \"In vitro binding assays (GST pulldown); LexA fusion transcriptional activation assays in yeast\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding assay plus functional activation assay; replicated in subsequent studies\",\n      \"pmids\": [\"7972120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"GCN5 and ADA2 (yeast) interact physically (co-immunoprecipitation in vitro and yeast two-hybrid in vivo) and function in the same complex or pathway (no additive effects in gcn5 ada2 double mutants). Both are required for VP16- and GCN4-dependent activation. The bromodomain of GCN5 is functionally important for transcriptional activation but not for ADA2 binding.\",\n      \"method\": \"Yeast two-hybrid assay; co-immunoprecipitation; gcn5 ada2 double-mutant epistasis analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP plus genetic epistasis; independently confirmed by multiple laboratories\",\n      \"pmids\": [\"7957049\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"ADA2 (yeast) physically interacts with TBP (TATA-binding protein) but not TFIIB. In yeast nuclear extracts, the association of VP16 activation domain with TBP (but not TFIIB) is dependent on ADA2. The N-terminus of ADA2 directly binds VP16, while ADA2 also interacts with GCN4 activation domain but not HAP4. These physical interactions correlate with ADA2's functional selectivity in vivo.\",\n      \"method\": \"GST pulldown with recombinant proteins; co-immunoprecipitation from yeast nuclear extracts; domain mapping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal binding assays (recombinant pulldown + nuclear extract co-IP) with domain mapping\",\n      \"pmids\": [\"7642611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"ADA2, ADA3, and GCN5 form a heterotrimeric complex in vitro, with ADA2 serving as the linchpin that holds ADA3 and GCN5 together. The C-terminal domain of ADA3 alone is sufficient for heterotrimeric complex formation in vitro and for ADA2-dependent activation in vivo. Activation by LexA-ADA3 fusions is regulated by ADA2 levels, and LexA-ADA2 fusion activation is regulated by ADA3 levels, indicating they form a complex in cells.\",\n      \"method\": \"In vitro complex reconstitution; LexA fusion transcriptional assays in yeast; ADA3 domain deletion analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of trimeric complex with domain dissection, replicated across labs\",\n      \"pmids\": [\"7862114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Genetic evidence confirms GCN5 and ADA2 interact and define one complex mediating transcriptional activation in yeast. LexA-GCN5 activates transcription only in the presence of wild-type ADA2 (and vice versa), and the bromodomain of GCN5 is required for this complex function. gcn5 ada2 double disruption shows no additive effects.\",\n      \"method\": \"Genetic epistasis (double disruption); LexA-fusion transcription activation assays in yeast\",\n      \"journal\": \"Molecular & general genetics : MGG\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis plus functional transcription assay; single lab but consistent with other studies\",\n      \"pmids\": [\"7898440\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Human ADA2 (hADA2, later designated hADA2α/TADA2A) was identified as a functional homolog of yeast ADA2. hADA2 interacts with hGCN5 in the yeast two-hybrid assay (and hGCN5 interacts with yADA2), contains a cryptic activation domain, and augments GAL4-VP16 activation in human HeLa cells. GAL4-hADA2 fusion activates transcription in HeLa cells, demonstrating functional conservation in human cells.\",\n      \"method\": \"Yeast two-hybrid assay; transient transfection in HeLa cells; sequence conservation analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — two-hybrid interaction plus functional transcription activation in human cells; foundational identification of human TADA2A\",\n      \"pmids\": [\"8552087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"In yeast, NGG1p/ADA3p and ADA2p are co-immunoprecipitated from whole-cell extracts, with <2% of ADA2p not associated with NGG1p, demonstrating near-complete association in vivo. Stability of each protein depends on the presence of the other. ADA2/ADA3-containing complexes exist in multiple sizes (>2 MDa, ~900 kDa, ~200 kDa) by ion-exchange and gel-filtration chromatography, and at least one complex associates with TBP via residues 274–307 of NGG1p/ADA3.\",\n      \"method\": \"Co-immunoprecipitation from yeast whole-cell extracts; ion-exchange and gel-filtration chromatography; stability assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP plus biochemical fractionation showing multiple native complexes\",\n      \"pmids\": [\"9038164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"GCN5 HAT activity is functionally linked to ADA2 interaction in vivo: the minimal catalytic HAT domain of GCN5 is necessary but not sufficient for full in vivo function — interaction with ADA2 is additionally required for complementation of growth and transcriptional activation in gcn5 mutant cells. LexA-GCN5 fusion activates transcription requiring both the HAT domain and the ADA2-interaction domain.\",\n      \"method\": \"Domain deletion mutagenesis of GCN5; complementation assays in gcn5 yeast; LexA-GCN5 transcription activation assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis combined with functional complementation and transcription assays\",\n      \"pmids\": [\"9034338\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"ADA1 was identified as an additional component of the ADA/GCN5 complex (~2 MDa). ADA1 interacts with other ADA proteins as shown by partial purification and co-immunoprecipitation. ada1 mutants show broader transcriptional defects than ada2/ada3/gcn5 mutants, suggesting the ADA/GCN5 complex has two separable functional modules.\",\n      \"method\": \"Co-immunoprecipitation; partial biochemical purification; transcriptional reporter assays in yeast\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP plus functional genetic evidence; single lab\",\n      \"pmids\": [\"9154821\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"TADA2A (human TADA2L/hADA2α) and GCN5L2 co-localize to chromosome 17q12–q21 by FISH and display similar tissue expression patterns across human tissues by Northern blot, suggesting coordinated regulation consistent with their functional interaction in a conserved complex.\",\n      \"method\": \"Fluorescence in situ hybridization (FISH); Northern blot analysis across human tissues\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — localization and expression data; no direct functional assay of the human protein\",\n      \"pmids\": [\"9073520\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Human GCN5 exists in a stable macromolecular complex (~67 Å Stokes radius, large complex) in human K562 erythroleukemia cells, but human ADA2 is resolved as a monomer (~35 Å) by gel-filtration chromatography, suggesting that unlike in yeast, human GCN5 and ADA2 are not stably associated with each other in a constitutive complex in this cell type.\",\n      \"method\": \"Gel-filtration chromatography of human K562 cell extracts; HAT activity fractionation\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical fractionation in human cells; single lab, single method\",\n      \"pmids\": [\"9398325\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"TADA2A (hADA2α) is a stable component of the human PCAF histone acetyltransferase complex, which contains more than 20 subunits including TAF subunits with histone fold motifs (hTAFII31, hTAFII20/15 — H3- and H2B-like). This establishes TADA2A as part of the human PCAF/SAGA-type coactivator complex.\",\n      \"method\": \"Affinity purification of the PCAF complex; mass spectrometry and peptide sequencing of subunits\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — affinity purification and mass spectrometry of native human complex; highly cited\",\n      \"pmids\": [\"9674425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Within the native human PCAF complex containing TADA2A, PCAF acetylates primarily lysine 14 of histone H3 and less efficiently lysine 8 of H4 on mononucleosomal substrates, and the complex polypeptides (including TADA2A/ADA2α) do not alter the substrate specificity of PCAF.\",\n      \"method\": \"In vitro HAT assay with mononucleosomes; Edman degradation of acetylated histones to identify acetylation sites\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic assay on nucleosomal substrate within native complex; single study\",\n      \"pmids\": [\"9880483\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Yeast Ada2 and Ada3 together with Gcn5 form the catalytic core of both the ADA and SAGA HAT complexes (the minimal module necessary and sufficient for nucleosomal HAT activity in vitro). Ada2 potentiates the Gcn5 catalytic activity; Ada3 facilitates nucleosomal acetylation and expanded lysine specificity. This catalytic core is necessary for nucleosomal HAT activity.\",\n      \"method\": \"Reconstitution of recombinant Ada2/Ada3/Gcn5 sub-complex; in vitro HAT assays on histones and nucleosomes; comparison with intact SAGA/ADA complexes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of catalytic module with nucleosomal HAT assays\",\n      \"pmids\": [\"11773077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The SANT domain of Ada2 (yeast) is required for normal histone acetylation by the SAGA complex in vivo and in vitro. Deletion and substitution mutations within the SANT domain of Ada2 and specific regions of the Gcn5 HAT domain (distinct from the catalytic site) impair substrate (histone/nucleosome) recognition. This identifies the Ada2 SANT domain as a histone/nucleosome substrate recognition module within SAGA.\",\n      \"method\": \"Site-directed mutagenesis of Ada2 SANT domain and Gcn5 HAT domain; in vitro HAT assays; in vivo histone acetylation assays in yeast\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis combined with in vitro and in vivo HAT activity assays\",\n      \"pmids\": [\"11777910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"A novel human Ada2 homologue, hADA2β (distinct from hADA2α/TADA2A), was identified. hADA2β interacts selectively with the Gcn5-containing TFTC/STAGA complex but not stably with the PCAF complex (which contains hADA2α). hADA2β (but not ADA2α) also associates with human Swi/Snf via Baf57 interaction, and functions with Gcn5 (but not PCAF) or Brg1 to coactivate Pax5/BSAP-dependent transcription. This establishes TADA2A (hADA2α) as the specific ADA2 isoform in the PCAF complex.\",\n      \"method\": \"Yeast two-hybrid screen; in vitro co-immunoprecipitation; transient transfection coactivation assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal assays defining distinct complex membership of TADA2A vs. TADA2B\",\n      \"pmids\": [\"12972612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"In Drosophila, there are two Ada2 homologs (dAda2a and dAda2b) that reside in distinct GCN5-containing complexes. dAda2b is a component of dSAGA (~2 MDa), while dAda2a associates with dGcn5 in a smaller (~0.8 MDa) complex not incorporated into dSAGA. dAda2a-containing complexes concentrate at transcriptionally active regions on polytene chromosomes independently of dSAGA. Humans and mice also possess two Ada2 variants with high homology to dAda2a (→ TADA2A) and dAda2b (→ TADA2B), suggesting the mammalian homologs form two functionally distinct subgroups.\",\n      \"method\": \"Biochemical fractionation (glycerol gradient sedimentation, chromatography); immunoprecipitation; immunofluorescence on polytene chromosomes\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal biochemical and cell biological approaches; two independent Drosophila studies (PMIDs 12697829 and 12482983) reached the same conclusion\",\n      \"pmids\": [\"12697829\", \"12482983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In Drosophila, Ada2a (ortholog of human TADA2A) null mutants are late-larva lethal and show a distinct phenotype from Ada2b null mutants. Ada2a null mutation does not reduce histone H3 K14/K9 acetylation or TAF10 localization (unlike Ada2b null), indicating Ada2a and Ada2b have non-redundant, distinct functions. Ada2a null impairs cell proliferation and differentially affects specific gene expression (e.g., rosy gene) and Dmp53-mediated apoptosis.\",\n      \"method\": \"Loss-of-function Drosophila genetics (null alleles); phenotypic analysis; histone acetylation assays by western blot; TAF10 localization by immunostaining\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean null alleles with defined phenotypic readouts including histone modification levels\",\n      \"pmids\": [\"16135810\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The 5' boundary of ACACA lies within a CpG island harboring a bidirectional promoter shared with the divergently oriented TADA2L (TADA2A) gene. This shared promoter coregulates transcripts for TADA2L and ACACA asymmetrically across human and mouse tissues, with RNA Pol II concentration in the intergenic region reflecting transcript abundance in brain vs. liver. This defines the genomic context of TADA2A transcription regulation.\",\n      \"method\": \"5' RACE; genomic sequencing; RNA Pol II ChIP in mouse tissues; Northern blot\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — ChIP and expression analysis of shared promoter; no direct functional assay of TADA2A protein\",\n      \"pmids\": [\"15607423\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Polyglutamine-expanded ataxin-7 is an integral subunit of the mammalian STAGA complex (which contains TADA2A/ADA2α). Poly(Q)-expanded ataxin-7 in STAGA dominantly inhibits GCN5-mediated nucleosomal histone acetylation in vitro and in SCA7 transgenic mice (by ChIP). TADA2A is thus a component of the human STAGA coactivator complex that can be functionally compromised in spinocerebellar ataxia type 7.\",\n      \"method\": \"Affinity purification of human STAGA; in vitro nucleosomal HAT assays; chromatin immunoprecipitation (ChIP) from SCA7 transgenic mouse retina\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — native complex purification, in vitro HAT assay, and in vivo ChIP in transgenic mouse model\",\n      \"pmids\": [\"15932940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"In Drosophila, dAda2a (TADA2A ortholog) and dGcn5 genetically interact: loss of either causes similar chromosome structural defects and developmental abnormalities. In dAda2a mutants, nucleosomal H4 acetylation at K12 and K5 is significantly reduced while H3 K9/K14 acetylation (established by dAda2b-containing complexes) is unaffected. This establishes that the TADA2A-type Ada2 (dAda2a) directs Gcn5 toward H4 lysine acetylation specifically.\",\n      \"method\": \"Drosophila loss-of-function genetics; histone acetylation analysis by western blot (antibodies to H4K12ac, H4K5ac, H3K9ac, H3K14ac); chromosome squash analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic analysis with specific histone modification readouts distinguishing two Ada2 paralogs\",\n      \"pmids\": [\"17030603\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Recombinant yeast Ada2/Ada3/Gcn5 sub-complex (the SAGA HAT module) was expressed and purified as a functional unit sufficient for acetylation of histones H3 and H2B on nucleosomes in vitro. BL21-CodonPlus E. coli strain enhanced purity of the metal-affinity-purified Ada2/Ada3/Gcn5 complex. This reconstituted complex serves as the minimal functional HAT module.\",\n      \"method\": \"Recombinant protein expression and purification; in vitro nucleosomal HAT assays\",\n      \"journal\": \"Methods (San Diego, Calif.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of minimal HAT module with nucleosomal substrate; methods paper\",\n      \"pmids\": [\"17309836\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"GCN5 and PCAF (both associated with TADA2A/ADA2α vs. ADA2β isoforms respectively in distinct complexes) function as co-activators in at least two types of human multiprotein complexes: STAGA-type (~2 MDa) and ATAC-type (~700 kDa). These complexes possess both global histone acetylation activity and gene-specific coactivator functions.\",\n      \"method\": \"Biochemical purification; mass spectrometry; HAT activity assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — review integrating biochemical purification data from multiple studies; TADA2A identity in these complexes established\",\n      \"pmids\": [\"17694077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Human ATAC (Ada Two-A containing) complex was purified and characterized; it contains ADA2-A (TADA2A), ADA3, STAF36, WDR5, POLE3/CHRAC17, POLE4, TAK1/MAP3K7, MBIP, and a novel YEATS2–NC2β histone fold module that interacts with TBP and negatively regulates transcription. TADA2A is thus a defining subunit of the human ATAC complex distinct from STAGA.\",\n      \"method\": \"Affinity purification of human ATAC complex from HeLa cells; mass spectrometry identification of subunits; TBP interaction assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — native complex purification and mass spectrometry; defines TADA2A as core ATAC subunit\",\n      \"pmids\": [\"18838386\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"A conserved ~120-amino-acid central region of yeast Ada2 (the 'RLR' region) is required for normal Gcn5 HAT activity. The ada2-RLR allele (R211S, L212A, R215A) reduces Gcn5-mediated histone acetylation in vitro to ~40% of wild-type and nearly eliminates in vivo acetylation of H2B K16, while reducing H3 K9/K18 acetylation to ~40%. This region also binds phospholipids (phosphatidylserine), suggesting a possible regulatory interaction.\",\n      \"method\": \"Site-directed mutagenesis; in vitro HAT assays; in vivo chromatin histone acetylation at Ada2-regulated promoters; microarray expression analysis; phospholipid binding assay\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis combined with in vitro and in vivo histone acetylation assays\",\n      \"pmids\": [\"18950642\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Ada2 (yeast) has a novel function in transcriptional silencing at telomeres and ribosomal DNA, distinct from its role in Gcn5-mediated activation. Ada2 binds telomeric chromatin and the silencing protein Sir2 in vivo (ChIP). Loss of ADA2 causes spreading of Sir2 and Sir3 into subtelomeric regions and decreased histone H4 K16 acetylation. Upon nutritional changes, Ada2 occupancy increases at subtelomeric regions adjacent to SAGA-inducible genes, derepressing silenced reporters.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) for Ada2, Sir2, Sir3 at telomeres and rDNA; in vivo silencing assays (telomeric reporter); histone modification analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP with functional silencing assays; single lab\",\n      \"pmids\": [\"19737915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Ada2 and Spt20 undergo co-translational assembly in yeast, dependent on the Ccr4-Not complex subunit Not5. SAGA mRNAs encoding a core set of subunits (including Ada2) are tethered together for co-translational assembly. Disruption of this co-translational assembly (via not5 deletion) impairs SAGA integrity, reducing histone acetylation.\",\n      \"method\": \"mRNA co-immunoprecipitation; polysome profiling; SAGA complex integrity assays; histone acetylation assays in yeast not5 mutants\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mRNA-protein association assays plus functional complex integrity readout; single lab\",\n      \"pmids\": [\"28180299\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Ada2(Gcn5)-dependent histone H3K14 acetylation (along with Sas3) is required for transcription elongation at the de-repressed FLO1 gene in yeast. In the absence of H3K14 acetylation, Swi/Snf recruitment and histone eviction proceed but RNAP II is absent from the coding region, demonstrating that Ada2-dependent H3 acetylation is required specifically for the transition from initiation to elongation.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) for RNAP II, Swi/Snf, histone modifications; transcription kinetics assays in histone mutant and ada2 yeast strains\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP-based mechanistic dissection of elongation vs. initiation; single lab\",\n      \"pmids\": [\"28115623\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Crystal structures of a yeast Ada2/Gcn5 complex were determined using Fab antibody crystallization chaperones. Structural and biochemical analysis revealed that the Ada2 SANT domain activates Gcn5 HAT activity not by directly affecting histone peptide binding as previously proposed, but by enhancing Gcn5 binding to the enzymatic co-substrate acetyl-CoA. This suggests a mechanism for regulating chromatin modification enzyme activity by controlling co-substrate rather than substrate binding.\",\n      \"method\": \"X-ray crystallography of Ada2/Gcn5 complex; in vitro HAT activity assays; acetyl-CoA binding assays; mutagenesis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure combined with biochemical activity and binding assays and mutagenesis\",\n      \"pmids\": [\"30224453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Large-scale yeast two-hybrid screening of human proteins detected protein-protein interactions involving TADA2A (TADA2L), placing it in the human binary interactome network and identifying novel interaction partners consistent with its role in coactivator complexes.\",\n      \"method\": \"High-throughput yeast two-hybrid assay (CCSB-HI1 dataset); co-affinity purification validation\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — high-throughput screen; TADA2A interactions not individually validated\",\n      \"pmids\": [\"16189514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The Ada2/Ada3/Gcn5/Sgf29 HAT module of SAGA is the minimal unit for Gcn5-mediated histone H3 acetylation at multiple positions. Structural and biochemical studies demonstrate that Ada2 activates Gcn5's intrinsically weak HAT activity, Ada3 facilitates nucleosomal acetylation and expanded lysine specificity, and Sgf29 binds H3K4me3 to recruit the module to active gene promoters. Two Ada2 isoforms (TADA2A and TADA2B) define distinct SAGA-related complexes with different histone substrate preferences.\",\n      \"method\": \"Review integrating structural studies, reconstitution biochemistry, and genetic data from multiple laboratories\",\n      \"journal\": \"Biochimica et biophysica acta. Gene regulatory mechanisms\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — review synthesizing multiple independent structural, biochemical, and genetic studies\",\n      \"pmids\": [\"32890768\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TADA2A (human ADA2α) is a transcriptional adaptor and core subunit of the PCAF/STAGA and ATAC histone acetyltransferase complexes, where it bridges acidic activation domains (VP16, GCN4) with TBP and potentiates GCN5/PCAF catalytic activity by enhancing acetyl-CoA binding via its SANT domain, enabling nucleosomal histone H3/H4 acetylation and transcription elongation; it is distinct from the paralogous TADA2B (ADA2β), which resides in SAGA-type complexes and directs H3K9/K14 acetylation, whereas TADA2A-containing complexes (ATAC) preferentially direct H4K5/K12 acetylation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TADA2A is a transcriptional adaptor protein that serves as the central scaffold of the histone acetyltransferase (HAT) module within GCN5/KAT2A-containing coactivator complexes, bridging GCN5 to ADA3 and connecting promoter-bound acidic activation domains to the general transcription machinery via direct interaction with TBP [PMID:7862114, PMID:7642611]. Its SANT domain stimulates GCN5 catalytic activity by enhancing binding of the cosubstrate acetyl-CoA rather than the histone substrate, thereby promoting nucleosomal H3 and H2B acetylation [PMID:30224453, PMID:11773077]. In metazoans, two paralogous Ada2 proteins define biochemically distinct complexes: TADA2A is a stable subunit of the PCAF acetyltransferase complex, whereas its paralog TADA2B resides in the TFTC/STAGA complex, and the two cannot substitute for each other [PMID:12972612, PMID:16135810]. In Drosophila, the TADA2A ortholog (dAda2a) specifically directs histone H4 K5 and K12 acetylation and is essential for viability [PMID:17030603, PMID:16135810].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Establishing that a dedicated adaptor exists between acidic activation domains and the basal transcription machinery resolved how certain activators (VP16, GCN4) stimulate transcription through an intermediary rather than by direct TFIID contact.\",\n      \"evidence\": \"Genetic screen for suppressors of GAL4-VP16 toxicity in yeast, plus in vitro transcription with ada2-mutant extracts\",\n      \"pmids\": [\"1638630\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No physical interaction partner identified\", \"Mechanism of selectivity for acidic vs. non-acidic activators unknown\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstrating that ADA2 directly binds both VP16 activation domains (via its N-terminus) and GCN5 established the physical basis for the adaptor model and placed ADA2 at the center of a coactivator complex.\",\n      \"evidence\": \"GST pulldown with VP16 peptides, yeast two-hybrid and co-immunoprecipitation of ADA2–GCN5, double-mutant epistasis\",\n      \"pmids\": [\"7972120\", \"7957049\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ADA3 role in the complex not yet defined\", \"No HAT activity link established\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Reconstitution of the ADA2/ADA3/GCN5 trimeric complex with ADA2 as the central linchpin, combined with the discovery that ADA2 also directly binds TBP, defined the minimal architecture connecting activators to the general transcription machinery.\",\n      \"evidence\": \"In vitro reconstitution of trimeric complex, co-IP of TBP from yeast nuclear extracts, domain mapping\",\n      \"pmids\": [\"7862114\", \"7642611\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ADA2 potentiates GCN5 enzymatic activity not yet tested\", \"Role of SANT domain uncharacterized\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Showing that GCN5's ADA2-interaction domain is required for in vivo function beyond its catalytic activity linked the adaptor role of ADA2 to transcriptional outcomes mediated by histone acetylation.\",\n      \"evidence\": \"Systematic GCN5 domain mutagenesis with in vivo complementation and transcriptional activation assays in yeast\",\n      \"pmids\": [\"9034338\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No direct demonstration that ADA2 stimulates HAT activity biochemically\", \"Nucleosomal substrate specificity not addressed\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Biochemical reconstitution proved that the Ada2/Ada3/Gcn5 trimer constitutes a minimal HAT module sufficient for nucleosomal acetylation of H3 and H2B, with Ada2 potentiating Gcn5 catalytic activity, answering whether Ada2 directly stimulates enzymatic function.\",\n      \"evidence\": \"Reconstituted trimeric complex tested in in vitro HAT assay on nucleosomal substrates\",\n      \"pmids\": [\"11773077\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of Ada2 potentiation (SANT domain vs. other regions) not resolved\", \"Histone lysine specificity determinants unknown\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identifying the SANT domain as the element required for nucleosomal histone acetylation narrowed the mechanism of Ada2-mediated stimulation to a specific structural module, initially attributed to substrate recognition.\",\n      \"evidence\": \"SANT domain deletion/substitution mutagenesis with in vitro and in vivo HAT assays\",\n      \"pmids\": [\"11777910\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SANT domain acts on substrate or cosubstrate binding not distinguished\", \"Central region function unknown\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Discovery of two metazoan Ada2 paralogs—TADA2A in the PCAF complex and TADA2B in TFTC/STAGA—resolved the paradox of apparently contradictory biochemical associations and established that distinct Ada2 isoforms define functionally non-redundant GCN5-containing complexes.\",\n      \"evidence\": \"Biochemical fractionation, co-IP, and yeast two-hybrid in Drosophila and human cells; independent identification by two labs\",\n      \"pmids\": [\"12697829\", \"12972612\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate specificities of TADA2A- vs. TADA2B-containing complexes not compared in mammalian cells\", \"Whether the two complexes regulate distinct gene sets in mammals untested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrating that loss of dAda2a specifically reduces H4 K5/K12 acetylation (while dAda2b controls H3 K9/K14 acetylation) established that Ada2 paralogs direct distinct histone substrate specificities in vivo.\",\n      \"evidence\": \"Drosophila Ada2a null mutant analysis with site-specific histone acetylation antibodies\",\n      \"pmids\": [\"17030603\", \"16135810\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mammalian TADA2A directs the same H4 specificity not tested\", \"Structural basis for paralog-specific substrate selectivity unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Fine mapping of a conserved central region in Ada2 (including residues R211/L212/R215) that regulates Gcn5 HAT activity and binds phospholipids revealed an additional functional domain beyond the SANT domain and suggested regulatory inputs from membrane lipid signaling.\",\n      \"evidence\": \"Clustered alanine mutagenesis, in vitro HAT assays, ChIP for acetylation marks, phospholipid binding assay in yeast\",\n      \"pmids\": [\"18950642\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance of phospholipid binding unresolved\", \"Whether this region functions similarly in metazoan TADA2A untested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrating that Ada2 promotes transcriptional silencing boundaries at telomeres via binding to telomeric chromatin and Sir2 revealed a function distinct from its canonical coactivation role, broadening the scope of Ada2 biology.\",\n      \"evidence\": \"ChIP of Ada2 at telomeres, co-IP with Sir2, silencing reporter assays, H4 K16 acetylation analysis in yeast\",\n      \"pmids\": [\"19737915\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mammalian TADA2A has analogous boundary/silencing functions unknown\", \"Mechanism by which Ada2 restricts Sir spreading not fully elucidated\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Crystal structures of the Ada2/Gcn5 complex definitively established that the Ada2 SANT domain stimulates Gcn5 HAT activity by enhancing acetyl-CoA cosubstrate binding rather than histone substrate binding, correcting the earlier model attributing SANT domain function to substrate recognition.\",\n      \"evidence\": \"X-ray crystallography using Fab chaperones, biochemical acetyl-CoA and histone peptide binding assays\",\n      \"pmids\": [\"30224453\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of full HAT module with nucleosomal substrate not available\", \"Whether Ada2 central region and SANT domain cooperate structurally unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The specific gene targets and biological processes regulated by mammalian TADA2A (as opposed to TADA2B) remain poorly defined, and no structural or functional characterization of the human TADA2A-containing PCAF complex HAT module has been reported.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No genome-wide target analysis for TADA2A-specific regulation in mammalian cells\", \"No structure of the mammalian TADA2A/GCN5 or TADA2A/PCAF complex\", \"Phenotypic consequences of TADA2A loss in mammalian systems not reported\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 1, 5, 7]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [11, 18, 21]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3, 4, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [6, 12, 19]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [12, 19]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [10, 11, 16, 18, 21]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 1, 5, 7]}\n    ],\n    \"complexes\": [\n      \"PCAF complex\",\n      \"ADA complex\",\n      \"SAGA complex\"\n    ],\n    \"partners\": [\n      \"KAT2A\",\n      \"TADA3\",\n      \"TBP\",\n      \"KAT2B\",\n      \"SGF29\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"TADA2A is a transcriptional adaptor protein that serves as a core scaffolding subunit of the PCAF, STAGA, and ATAC histone acetyltransferase complexes, where it bridges acidic activation domains of transcription factors (VP16, GCN4) with TBP and potentiates GCN5/PCAF-mediated histone acetylation [PMID:1638630, PMID:7642611, PMID:9674425, PMID:18838386]. Within the catalytic HAT module formed by Ada2/Ada3/Gcn5, TADA2A activates the intrinsically weak acetyltransferase activity of GCN5 through its SANT domain, which enhances acetyl-CoA co-substrate binding rather than histone substrate recognition [PMID:30224453, PMID:11773077]. TADA2A-containing complexes (ATAC) preferentially direct histone H4 K5/K12 acetylation, distinguishing them from the paralogous TADA2B-containing SAGA-type complexes that target H3 K9/K14, and this Ada2-dependent acetylation is required for the transition from transcription initiation to elongation [PMID:17030603, PMID:28115623]. Polyglutamine-expanded ataxin-7 incorporated into TADA2A-containing STAGA dominantly inhibits nucleosomal histone acetylation, linking TADA2A complex dysfunction to spinocerebellar ataxia type 7 [PMID:15932940].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Establishing that a dedicated coactivator exists between acidic activators and the basal transcription machinery: yeast ADA2 was identified as a selective transcriptional adaptor required for VP16/GCN4-dependent activation but dispensable for basal transcription, founding the concept of activation-domain-specific coactivators.\",\n      \"evidence\": \"Genetic selection for GAL4-VP16 toxicity resistance in yeast; in vitro transcription with ada2 mutant extracts\",\n      \"pmids\": [\"1638630\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of selectivity for acidic vs. other activation domains unknown\", \"No biochemical identity of the complex or direct interactors\", \"Mammalian relevance unaddressed\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Defining ADA2 as a physical scaffold linking activators to the HAT enzyme GCN5: ADA2 directly binds the VP16 activation domain and physically interacts with GCN5, with epistasis showing they function in the same pathway, establishing the adaptor-HAT connection.\",\n      \"evidence\": \"GST pulldown binding assays; yeast two-hybrid; co-immunoprecipitation; gcn5/ada2 double-mutant epistasis\",\n      \"pmids\": [\"7972120\", \"7957049\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and full composition of native complex unknown\", \"Whether ADA2 contacts TBP directly not yet tested\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Resolving the trimeric core and dual bridging function: ADA2 forms a heterotrimeric complex with ADA3 and GCN5 (ADA2 as linchpin), and ADA2 also directly contacts TBP, establishing it as a bidirectional bridge between activator–HAT and the basal machinery.\",\n      \"evidence\": \"In vitro reconstitution of Ada2/Ada3/Gcn5 trimer; GST pulldown and co-IP for ADA2–TBP interaction; domain mapping\",\n      \"pmids\": [\"7862114\", \"7642611\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Native complex size and additional subunits unknown\", \"Whether ADA2–TBP interaction is direct in the context of a larger complex\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Demonstrating evolutionary conservation in humans: human ADA2α (TADA2A) was cloned and shown to interact with hGCN5 and augment VP16-dependent activation in HeLa cells, establishing functional conservation from yeast to mammals.\",\n      \"evidence\": \"Yeast two-hybrid for hADA2–hGCN5 interaction; transient transfection transcription assays in HeLa cells\",\n      \"pmids\": [\"8552087\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the native human complex containing TADA2A unknown\", \"Whether mammalian ADA2α is stably complexed with GCN5 in vivo unresolved\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Placing TADA2A in a defined macromolecular coactivator complex: TADA2A was identified as a stable subunit of the human PCAF HAT complex (~20 subunits including TAF-like histone fold proteins), defining its physiological context.\",\n      \"evidence\": \"Affinity purification of native PCAF complex from human cells; mass spectrometry subunit identification\",\n      \"pmids\": [\"9674425\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TADA2A also exists in non-PCAF complexes in human cells\", \"Functional role of TADA2A within the PCAF complex not biochemically dissected\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identifying Ada2 as essential for nucleosomal HAT activity: reconstitution showed Ada2/Ada3/Gcn5 is the minimal catalytic HAT module sufficient for nucleosomal acetylation, with Ada2 potentiating Gcn5 catalytic activity.\",\n      \"evidence\": \"Recombinant sub-complex reconstitution; in vitro HAT assays on nucleosomal substrates\",\n      \"pmids\": [\"11773077\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which Ada2 potentiates Gcn5 activity unresolved at atomic level\", \"Whether this applies to mammalian TADA2A–GCN5 not directly tested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identifying the SANT domain as the functional element: mutations in the Ada2 SANT domain impaired histone acetylation in vitro and in vivo, establishing this domain as a histone/nucleosome recognition element within the HAT module.\",\n      \"evidence\": \"Site-directed mutagenesis of Ada2 SANT domain; in vitro and in vivo HAT assays in yeast\",\n      \"pmids\": [\"11777910\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the SANT domain contacts histones directly or acts allosterically on Gcn5 unclear\", \"Structural basis of SANT domain function not determined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Establishing paralog-specific complex membership: identification of TADA2B (hADA2β) demonstrated that TADA2A resides selectively in PCAF-type complexes while TADA2B resides in STAGA/TFTC-type complexes, with non-overlapping functions in coactivation.\",\n      \"evidence\": \"Yeast two-hybrid; co-immunoprecipitation; transient transfection coactivation assays in mammalian cells; Drosophila biochemical fractionation\",\n      \"pmids\": [\"12972612\", \"12697829\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TADA2A and TADA2B have distinct histone substrate specificities in mammalian cells\", \"Structural basis for paralog-specific complex incorporation unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Resolving histone substrate specificity: Drosophila Ada2a (TADA2A ortholog) null mutants showed selective loss of H4 K5/K12 acetylation while H3 K9/K14 acetylation was unaffected, demonstrating that the TADA2A-type adaptor directs the HAT toward H4 lysines specifically.\",\n      \"evidence\": \"Drosophila null alleles; histone modification-specific western blots; chromosome structural analysis\",\n      \"pmids\": [\"17030603\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this substrate specificity is conserved in mammalian TADA2A-containing complexes\", \"Structural mechanism by which Ada2a redirects Gcn5 to H4 unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defining the ATAC complex: human ATAC was purified and shown to contain TADA2A as a defining subunit alongside ADA3, WDR5, YEATS2, and other components, establishing ATAC as a distinct TADA2A-specific complex separate from STAGA.\",\n      \"evidence\": \"Affinity purification from HeLa cells; mass spectrometry; TBP interaction assays\",\n      \"pmids\": [\"18838386\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Genomic targets and biological functions of ATAC vs. STAGA in human cells not dissected\", \"Regulation of ATAC assembly and recruitment unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Revealing the structural mechanism of Ada2-mediated HAT activation: crystal structures of Ada2/Gcn5 showed that the Ada2 SANT domain enhances Gcn5 activity by promoting acetyl-CoA co-substrate binding rather than by improving histone substrate recognition, revising the prior model.\",\n      \"evidence\": \"X-ray crystallography of Ada2/Gcn5 complex; acetyl-CoA binding assays; mutagenesis and in vitro HAT assays\",\n      \"pmids\": [\"30224453\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of full Ada2/Ada3/Gcn5 HAT module on nucleosomal substrate not yet determined\", \"Whether acetyl-CoA sensing by Ada2 constitutes a metabolic regulatory mechanism in vivo\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The genomic targets and functional consequences of TADA2A-containing ATAC complex activity in mammalian cells, and whether TADA2A loss-of-function causes human disease, remain to be established through direct human genetic and functional genomic studies.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No human genetic disease directly linked to TADA2A mutations in the literature\", \"Genome-wide binding and acetylation targets of human ATAC complex not mapped\", \"Role of TADA2A in mammalian development and tissue-specific gene regulation unexplored\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 2, 7, 9, 15]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [16, 30, 32]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 4, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [8, 13, 18, 27]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [18, 22, 27]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [15, 16, 22, 30, 32]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 7, 9, 29]}\n    ],\n    \"complexes\": [\n      \"PCAF complex\",\n      \"STAGA complex\",\n      \"ATAC complex\",\n      \"Ada2/Ada3/Gcn5 HAT module\"\n    ],\n    \"partners\": [\n      \"GCN5\",\n      \"PCAF\",\n      \"ADA3\",\n      \"YEATS2\",\n      \"WDR5\",\n      \"TBP\",\n      \"SGF29\",\n      \"ATXN7\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}