{"gene":"H2AC18","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":1980,"finding":"The histone octamer (H3)2(H4)2(H2A)2(H2B)2 has a 2-fold axis of symmetry and forms a left-handed helical spool; the (H3)2(H4)2 tetramer forms the central turn while two H2A-H2B dimers lie on each face, each associated with approximately half a turn of DNA.","method":"Image reconstruction by electron microscopy to 22 Å resolution combined with cross-linking studies","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — structural reconstruction with functional model, foundational finding widely replicated","pmids":["7422003"],"is_preprint":false},{"year":1980,"finding":"The nucleosomal core histone octamer dissociates asymmetrically: first releasing one H2A-H2B dimer to form a hexamer (H2A-H2B)-(H3)2-(H4)2, then releasing the second H2A-H2B dimer, leaving the (H3)2-(H4)2 tetramer. This dissociation is accelerated by increased temperature or decreased pH and is accompanied by conformational changes.","method":"Gel exclusion chromatography of isolated rat liver core histone octamer, monitored by histone composition and circular dichroism","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro reconstitution assay, single lab, single study","pmids":["7397178"],"is_preprint":false},{"year":1980,"finding":"H2A exists as at least eight protein species including H2A.1, H2A.2, H2A.X, and H2A.Z; all four variants are present in nucleosomal core particles; approximately 11% of each variant is conjugated to ubiquitin; the molar sum of all H2A species equals that of H4, H2B, or H3 in chromatin.","method":"SDS-PAGE, acetic acid-urea gels, nonionic detergent gels, isolation of nucleosomal core particles from mouse L1210 cells","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal gel systems, multiple cell/tissue types, foundational characterization replicated across labs","pmids":["7407044"],"is_preprint":false},{"year":1977,"finding":"H2A.2 and H2A.1 differ in primary structure (not post-synthetic modification of the same parent protein); H2A.2 contains a methionine critical to an antigenic difference that immunologically distinguishes it from H2A.1; antibodies against H2A.2 cross-react with H2A.1 but show higher specificity for H2A.2 at higher dilutions.","method":"Biochemical purification, amino acid analysis, immunological characterization with antibodies raised against purified H2A.2 subfraction","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical and immunological characterization using purified proteins, two orthogonal approaches","pmids":["562183"],"is_preprint":false},{"year":1981,"finding":"H2A.1 and H2A.2 have distinct organizational positions in chromatin: anti-H2A.1 IgG binds to intact chromatin and isolated nucleosomes, while anti-H2A.2 IgG does not bind, indicating that H2A.2-unique antigenic determinants are buried within the nucleosome core. H1-depleted, HMG-enriched nucleosomes react better with anti-H2A.1 than H1-containing nucleosomes.","method":"Radioimmunoassay using chromatin as immunoabsorbent and solid-phase binding of antibodies to nucleosome subfractions; antibodies directed against purified H2A.1 and H2A.2 variants","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal antibody binding assay with chromatin and nucleosome subfractions, multiple cell types tested","pmids":["7240246"],"is_preprint":false},{"year":1984,"finding":"H2A.1 and H2A.2 are synthesized and incorporated into chromatin at a significant rate even when DNA synthesis is inhibited, suggesting turnover of these histones independent of replication; H2A.1 has a higher turnover rate than H2A.2 in exponentially growing cells, a difference more pronounced in induced (differentiating) cells.","method":"Metabolic labeling with radioisotopes in murine erythroleukemia cells, pulse-chase analysis with DNA synthesis inhibitor, PAGE resolution of histone variants","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pulse-chase metabolic labeling with inhibitor controls, single lab","pmids":["6593094"],"is_preprint":false},{"year":1985,"finding":"H2A.2 synthesized in G1 phase is deposited onto chromatin (old DNA) rather than selectively onto newly replicated DNA, unlike H3 and H4 which deposit primarily on newly replicated DNA in S phase. H2A.2 deposits to a 2–4-fold lower extent in G1 compared to H1 and HMGs.","method":"Cell synchronization in G1 and S phase, radiolabeling, chromatin fractionation to separate new and old DNA, PAGE","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell synchronization with radiolabeled pulse, DNA fractionation, single lab with multiple conditions","pmids":["3935167"],"is_preprint":false},{"year":1986,"finding":"In Drosophila polytene chromosomes, H2A.2 localizes specifically to interbands (less compacted chromatin regions) as demonstrated by indirect immunofluorescence, whereas H2A.1 distributes throughout all chromosome regions, suggesting H2A.2 contributes to less compacted chromatin structure associated with gene-containing regions.","method":"Indirect immunofluorescence of polytene chromosomes using antibodies specific to H2A.1 and H2A.2","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization by immunofluorescence with variant-specific antibodies, tied to functional chromatin organization context","pmids":["2425354"],"is_preprint":false},{"year":1988,"finding":"BPDE-I (benzo[a]pyrene diol-epoxide) binding to H2A.2 occurs primarily at the C-terminal octapeptide region; the C-terminal histidine residues present in rat and chicken H2A (including H2A.2) but absent in Xenopus H2A are the likely nucleophilic targets for BPDE-I adduct formation.","method":"HPLC analysis of BPDE-I-labeled core histones from nuclei, V8-protease digestion, carboxypeptidase B treatment of modified H2A.2, in vitro reaction of isolated C-terminal peptides with BPDE-I","journal":"Carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro peptide modification assay with enzymatic mapping, multiple species comparison, single lab","pmids":["3125994"],"is_preprint":false},{"year":1991,"finding":"A coding region activating sequence (CRAS) in the H2a.2 gene (codons 50–85) is required for high-level expression; this element is orientation-dependent and position-independent; the same nuclear proteins interact with CRAS elements from both H2a.2 and H3.2 genes, indicating a common transcriptional regulatory factor for replication-dependent histone genes.","method":"In-frame deletion mutagenesis of H2a.2 coding region, stable transfection, gel mobility shift competition assays","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis + stable transfection + gel shift, single lab with multiple orthogonal approaches","pmids":["2038312"],"is_preprint":false},{"year":1994,"finding":"H2A.1 and H2A.2 variants in rat spermatids undergo post-translational modification between steps 3 and 7 of spermiogenesis, as demonstrated by PAGE analysis showing altered electrophoretic mobility of both H2A variants at those stages.","method":"Vitamin A-synchronized rat testes, centrifugal elutriation to obtain spermatids at specific steps 1-12, PAGE analysis of basic nucleoproteins","journal":"Biology of reproduction","confidence":"Low","confidence_rationale":"Tier 3 / Weak — PAGE-based detection of post-translational modification, single lab, modification type not identified","pmids":["7948489"],"is_preprint":false},{"year":1994,"finding":"H2A.2 is not ADP-ribosylated under normal conditions in sea urchin embryo nuclei at any developmental stage examined, but dimethylsulfate treatment induces poly-ADP-ribosylation of H2A.2 in embryos, indicating that ADP-ribosylation of H2A.2 is tightly regulated and suppressed during early development.","method":"2D-PAGE autoradiography of [32P]NAD+-labeled nuclei from sea urchin embryos, with and without dimethylsulfate treatment","journal":"Development, growth & differentiation","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single 2D-PAGE/autoradiography experiment in sea urchin (not mammalian), single lab","pmids":["37280829"],"is_preprint":false},{"year":2003,"finding":"Acetylation of the N-terminal tail of major H2A (H2A.1/H2A.2) in Tetrahymena is not essential for viability; however, the nonacetylatable N-terminal tail of major H2A can substitute for the essential acetylation function of the H2A.Z N-terminal tail, with the effects on viability determined by properties of the H2A core rather than the tail.","method":"In vitro mutagenesis of lysine residues + gene replacement in Tetrahymena thermophila, tail-swapping experiments between H2A.1/H2A.2 and H2A.Z","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — site-directed mutagenesis combined with in vivo gene replacement and tail-swap experiments, multiple orthogonal genetic tests","pmids":["12665578"],"is_preprint":false},{"year":2016,"finding":"HIST2H2AA3 (H2AC18) mRNA is expressed as a polyadenylated mRNA in terminally differentiated fibroblasts but not in serum-starved fibroblasts, indicating that polyadenylated expression of this replication-dependent histone gene is part of the terminal differentiation program rather than a simple response to cell cycle arrest.","method":"RNA-seq and RT-PCR analysis of differentiated vs. serum-starved fibroblasts; conservation analysis across mammalian species","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNA-seq with RT-PCR validation in differentiated cells, single lab with multiple conditions and conservation analysis","pmids":["27402160"],"is_preprint":false},{"year":2022,"finding":"H2AC18 pre-mRNA can be processed by two mutually exclusive pathways: either by the replication-dependent histone machinery (producing non-polyadenylated mRNA ending at the stem-loop) or by the canonical polyadenylation machinery (producing polyadenylated mRNA). This dual processing capability arises because the canonical polyadenylation signal (AAUAAA) overlaps with the histone downstream element (HDE); disruption of the PAS sequence prevents recruitment of the canonical complex without affecting histone machinery recruitment.","method":"In vitro pre-mRNA processing assays with purified complexes, PAS mutagenesis, RNA-binding complex recruitment assays","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution of processing complexes, mutagenesis of cis-acting elements, mechanistic dissection with multiple orthogonal approaches in single rigorous study","pmids":["36447390"],"is_preprint":false},{"year":2019,"finding":"In S. cerevisiae, CAG/CTG repeat stability depends on H2A.1 but not H2A.2; H2A.1 promotes high-fidelity homologous recombination, sister chromatid recombination, and break-induced replication through its unique Thr126 residue; hta1-T126A mutants are epistatic to deletion of Pol32 (Polδ subunit), placing H2A.1-Thr126 in the D-loop extension step of recombination. H2A.2 does not share these repair functions.","method":"Genetic analysis of CAG repeat stability in H2A copy mutants, epistasis analysis with pol32Δ, site-directed mutagenesis (T126A), sister chromatid recombination assays","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with mutagenesis in yeast, multiple repair assays, single lab; yeast H2A.2 ortholog context","pmids":["31804179"],"is_preprint":false},{"year":2017,"finding":"The H2A.2 (HIST2H2AA3) gene has a CpG island near its transcription start site; treatment with DNMT inhibitors increases H2A.2 expression while HDAC inhibitors also increase expression; methyl-DNA immunoprecipitation shows hyper-methylation of the H2A.2 promoter in embryonic and HCC tissue compared to control adult liver, indicating that DNA methylation dynamically regulates H2A.2 transcription across pathophysiological states.","method":"Transient transfection with dual luciferase reporter for cloned promoter sequences, DNMT/HDAC inhibitor treatment, methyl-DNA immunoprecipitation (MeDIP) coupled with qPCR, in silico CpG analysis","journal":"The international journal of biochemistry & cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — luciferase reporter + MeDIP + inhibitor experiments, multiple orthogonal approaches, single lab","pmids":["28163185"],"is_preprint":false}],"current_model":"H2AC18 (HIST2H2AA3/H2A.2) is a replication-dependent core histone that forms H2A-H2B dimers on each face of the (H3)2(H4)2 tetramer within the nucleosome octamer; its C-terminal histidine residues are sites of carcinogen (BPDE) adduct formation; its pre-mRNA undergoes mutually exclusive processing by either the histone stem-loop machinery or the canonical polyadenylation machinery through overlapping cis-elements; its expression in terminally differentiated cells occurs as polyadenylated mRNA as part of a differentiation program; and its promoter is subject to dynamic DNA methylation that regulates variant-specific transcription across proliferative and differentiation states."},"narrative":{"mechanistic_narrative":"H2AC18 (HIST2H2AA3/H2A.2) is a replication-dependent core histone of the H2A family that assembles into the nucleosome as part of an H2A-H2B dimer; two such dimers lie on each face of the (H3)2(H4)2 tetramer to complete the octamer that wraps DNA into the chromatin fiber [PMID:7422003, PMID:7407044]. H2A.2 is a distinct primary-sequence variant rather than a modified form of H2A.1, carrying variant-specific antigenic determinants and a critical methionine that immunologically distinguish it [PMID:562183]; its unique determinants are buried within the nucleosome core, indicating a distinct organizational position relative to H2A.1 [PMID:7240246]. Functionally, the two variants are non-equivalent: H2A.2 turns over more slowly than H2A.1, deposits onto bulk (old) DNA rather than selectively onto newly replicated DNA, and preferentially associates with less compacted, gene-containing interband chromatin [PMID:6593094, PMID:3935167, PMID:2425354]. The C-terminal histidine residues of H2A.2 are the principal nucleophilic targets for adduct formation by the carcinogen BPDE [PMID:3125994]. High-level transcription depends on a coding-region activating sequence (CRAS) bound by a factor shared with other replication-dependent histone genes [PMID:2038312], and the gene's promoter CpG island is subject to dynamic DNA methylation that modulates variant-specific expression across proliferative, embryonic, and hepatocellular carcinoma states [PMID:28163185]. Although replication-dependent, H2AC18 pre-mRNA can be processed by two mutually exclusive routes—the histone stem-loop machinery or the canonical polyadenylation machinery—because the polyadenylation signal overlaps the histone downstream element; polyadenylated expression occurs as part of a terminal differentiation program [PMID:27402160, PMID:36447390].","teleology":[{"year":1980,"claim":"Established the structural context in which H2A functions, showing how H2A-H2B dimers assemble onto the (H3)2(H4)2 tetramer to build the nucleosome and organize DNA.","evidence":"EM image reconstruction to 22 Å plus cross-linking of the histone octamer; gel-exclusion chromatography of isolated octamers monitored by CD","pmids":["7422003","7397178"],"confidence":"High","gaps":["Does not resolve variant-specific positioning of H2A.2 within the octamer","In vitro dissociation behavior not linked to a specific H2A variant"]},{"year":1980,"claim":"Defined H2A as a family of distinct protein species present together in core particles, framing the question of what distinguishes individual variants such as H2A.2.","evidence":"Multiple orthogonal gel systems on nucleosomal core particles from mouse L1210 cells","pmids":["7407044"],"confidence":"High","gaps":["Does not assign function to individual variants","Ubiquitin-conjugation fraction not mapped to specific variants"]},{"year":1977,"claim":"Demonstrated that H2A.2 is a genuine primary-sequence variant of H2A.1, not a post-synthetically modified form, with a unique methionine producing an antigenic difference.","evidence":"Biochemical purification, amino acid analysis, and immunological characterization with variant-specific antibodies","pmids":["562183"],"confidence":"Medium","gaps":["Antibody cross-reactivity limits absolute specificity","Functional consequence of the sequence difference not addressed"]},{"year":1981,"claim":"Showed that H2A.2 occupies a distinct organizational position in chromatin, its unique determinants buried within the nucleosome core unlike those of H2A.1.","evidence":"Reciprocal radioimmunoassay using chromatin and nucleosome subfractions with variant-specific antibodies","pmids":["7240246"],"confidence":"Medium","gaps":["Molecular basis of differential burial not defined","No direct structural assignment of H2A.2 placement"]},{"year":1984,"claim":"Revealed that H2A.2 has replication-independent turnover with kinetics distinct from H2A.1, more pronounced in differentiating cells, linking the variant to chromatin dynamics beyond S phase.","evidence":"Metabolic pulse-chase labeling with a DNA synthesis inhibitor in murine erythroleukemia cells","pmids":["6593094"],"confidence":"Medium","gaps":["Mechanism of replication-independent deposition not identified","Single cell system"]},{"year":1985,"claim":"Showed that G1-synthesized H2A.2 deposits onto pre-existing (old) DNA rather than newly replicated DNA, distinguishing its deposition behavior from H3 and H4.","evidence":"Cell synchronization, radiolabeling, and chromatin fractionation separating new and old DNA","pmids":["3935167"],"confidence":"Medium","gaps":["Chaperone/deposition machinery for H2A.2 not identified","Functional consequence of old-DNA deposition unresolved"]},{"year":1986,"claim":"Linked H2A.2 to chromatin architecture by showing its preferential localization to less-compacted, gene-containing interband regions, unlike the ubiquitous H2A.1.","evidence":"Indirect immunofluorescence of Drosophila polytene chromosomes with variant-specific antibodies","pmids":["2425354"],"confidence":"Medium","gaps":["Causal role in decompaction versus correlation not established","Drosophila context may not map directly to mammalian H2AC18"]},{"year":1988,"claim":"Identified the C-terminal histidine residues of H2A.2 as the nucleophilic targets of the carcinogen BPDE, implicating the variant in carcinogen-DNA/protein adduct chemistry.","evidence":"HPLC, V8/carboxypeptidase mapping of BPDE-labeled histones, and in vitro peptide reactions across species","pmids":["3125994"],"confidence":"Medium","gaps":["Biological consequence of adduct formation not determined","Single lab"]},{"year":1991,"claim":"Defined a coding-region activating sequence (CRAS) required for high-level H2a.2 transcription and bound by a factor shared with other replication-dependent histone genes, identifying a common regulatory mechanism.","evidence":"In-frame coding deletion mutagenesis, stable transfection, and gel mobility-shift competition assays","pmids":["2038312"],"confidence":"Medium","gaps":["Identity of the CRAS-binding factor not established","Mechanism of orientation-dependence unresolved"]},{"year":2003,"claim":"Tested the essentiality of major-H2A N-terminal acetylation, showing it is dispensable for viability and that the core, not the tail, dictates functional substitution for H2A.Z.","evidence":"Lysine mutagenesis, gene replacement, and tail-swap experiments in Tetrahymena","pmids":["12665578"],"confidence":"High","gaps":["Does not separate H2A.1 from H2A.2 contributions","Tetrahymena context"]},{"year":2016,"claim":"Showed that polyadenylated expression of this replication-dependent histone gene is a feature of the terminal differentiation program rather than mere cell-cycle arrest.","evidence":"RNA-seq and RT-PCR in differentiated versus serum-starved fibroblasts with cross-mammalian conservation analysis","pmids":["27402160"],"confidence":"Medium","gaps":["Functional role of the polyadenylated isoform not defined","Trans-factors driving the switch unidentified"]},{"year":2017,"claim":"Demonstrated that promoter CpG-island DNA methylation dynamically regulates H2A.2 transcription across embryonic, adult, and hepatocellular carcinoma states.","evidence":"Dual-luciferase promoter reporters, DNMT/HDAC inhibitor treatment, and MeDIP-qPCR","pmids":["28163185"],"confidence":"Medium","gaps":["Causal contribution to tumorigenesis not established","Methylation-sensitive transcription factors unidentified"]},{"year":2022,"claim":"Resolved how a single pre-mRNA can yield either histone-type or polyadenylated transcripts, showing the canonical PAS overlaps the histone downstream element so the two processing routes are mutually exclusive.","evidence":"In vitro processing assays with purified complexes, PAS mutagenesis, and complex-recruitment assays","pmids":["36447390"],"confidence":"High","gaps":["In vivo determinants of pathway choice not defined","Regulatory signals selecting between machineries unknown"]},{"year":null,"claim":"How H2A.2's distinct deposition, turnover, and chromatin localization translate into a specific genomic function, and what selects its dual pre-mRNA processing fate in vivo, remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No deposition chaperone identified for H2AC18","Genome-wide occupancy of the variant in mammalian cells not mapped","In vivo trigger for polyadenylated versus stem-loop processing unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,2]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[0,4,7]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[0,7]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[14]}],"complexes":["nucleosome"],"partners":["H2B","H3","H4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6FI13","full_name":"Histone H2A type 2-A","aliases":["H2A-clustered histone 18","H2A-clustered histone 19","Histone H2A.2","Histone H2A/o"],"length_aa":130,"mass_kda":14.1,"function":"Core component of nucleosome. Nucleosomes wrap and compact DNA into chromatin, limiting DNA accessibility to the cellular machineries which require DNA as a template. Histones thereby play a central role in transcription regulation, DNA repair, DNA replication and chromosomal stability. DNA accessibility is regulated via a complex set of post-translational modifications of histones, also called histone code, and nucleosome remodeling","subcellular_location":"Nucleus; Chromosome","url":"https://www.uniprot.org/uniprotkb/Q6FI13/entry"},"depmap":{"release":"DepMap","has_data":false,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/H2AC18"},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/H2AC18","total_profiled":1310},"omim":[{"mim_id":"142720","title":"HISTONE GENE CLUSTER 2, H2A HISTONE FAMILY, MEMBER A3; HIST2H2AA3","url":"https://www.omim.org/entry/142720"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"bone marrow","ntpm":82.0},{"tissue":"prostate","ntpm":54.7}],"url":"https://www.proteinatlas.org/search/H2AC18"},"hgnc":{"alias_symbol":["H2A.2","H2A/q"],"prev_symbol":["H2AFO","HIST2H2AA","HIST2H2AA3"]},"alphafold":{"accession":"Q6FI13","domains":[{"cath_id":"1.10.20.10","chopping":"18-110","consensus_level":"medium","plddt":97.8284,"start":18,"end":110}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6FI13","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6FI13-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6FI13-F1-predicted_aligned_error_v6.png","plddt_mean":91.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=H2AC18","jax_strain_url":"https://www.jax.org/strain/search?query=H2AC18"},"sequence":{"accession":"Q6FI13","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6FI13.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6FI13/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6FI13"}},"corpus_meta":[{"pmid":"7422003","id":"PMC_7422003","title":"A low resolution structure for the histone core of the nucleosome.","date":"1980","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/7422003","citation_count":259,"is_preprint":false},{"pmid":"7407044","id":"PMC_7407044","title":"Histone 2A, a heteromorphous family of eight protein species.","date":"1980","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/7407044","citation_count":246,"is_preprint":false},{"pmid":"2116362","id":"PMC_2116362","title":"A novel B-cell lineage-specific transcription factor present at early but not late stages of differentiation.","date":"1990","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/2116362","citation_count":213,"is_preprint":false},{"pmid":"8497273","id":"PMC_8497273","title":"NF-HB (BSAP) is a repressor of the murine immunoglobulin heavy-chain 3' alpha enhancer at early stages of B-cell differentiation.","date":"1993","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/8497273","citation_count":127,"is_preprint":false},{"pmid":"3622934","id":"PMC_3622934","title":"Changes in histones H2A and H3 variant composition in differentiating and mature rat brain cortical neurons.","date":"1987","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/3622934","citation_count":116,"is_preprint":false},{"pmid":"6593094","id":"PMC_6593094","title":"Regulation of nucleosomal core histone variant levels in differentiating murine erythroleukemia cells.","date":"1984","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/6593094","citation_count":71,"is_preprint":false},{"pmid":"10579635","id":"PMC_10579635","title":"Histone variants of H2A and H3 families are regulated during in vitro aging in the same manner as during differentiation.","date":"1999","source":"Experimental gerontology","url":"https://pubmed.ncbi.nlm.nih.gov/10579635","citation_count":66,"is_preprint":false},{"pmid":"3935167","id":"PMC_3935167","title":"Histone synthesis and deposition in the G1 and S phases of hepatoma tissue culture cells.","date":"1985","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/3935167","citation_count":65,"is_preprint":false},{"pmid":"27402160","id":"PMC_27402160","title":"A subset of replication-dependent histone mRNAs are expressed as polyadenylated RNAs in terminally differentiated tissues.","date":"2016","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/27402160","citation_count":60,"is_preprint":false},{"pmid":"8144891","id":"PMC_8144891","title":"The transcription factor BSAP (NF-HB) is essential for immunoglobulin germ-line epsilon transcription.","date":"1994","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/8144891","citation_count":56,"is_preprint":false},{"pmid":"833117","id":"PMC_833117","title":"Studies of human histone messenger RNA. II. The resolution of fractions containing individual human histone messenger RNA species.","date":"1977","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/833117","citation_count":50,"is_preprint":false},{"pmid":"562183","id":"PMC_562183","title":"Biochemical and immunological characterization of two distinct variants of histone H2A in Friend leukemia.","date":"1977","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/562183","citation_count":48,"is_preprint":false},{"pmid":"1101222","id":"PMC_1101222","title":"A model for chromatin structure.","date":"1975","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/1101222","citation_count":43,"is_preprint":false},{"pmid":"2744459","id":"PMC_2744459","title":"Developmental and tissue-specific regulation of a novel transcription factor of the sea urchin.","date":"1989","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/2744459","citation_count":43,"is_preprint":false},{"pmid":"8603674","id":"PMC_8603674","title":"Changes in core histone variant composition in differentiating neurons: the roles of differential turnover and synthesis rates.","date":"1995","source":"European journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/8603674","citation_count":42,"is_preprint":false},{"pmid":"34591994","id":"PMC_34591994","title":"Single-cell RNA-sequencing atlas of bovine caudal intervertebral discs: Discovery of heterogeneous cell populations with distinct roles in homeostasis.","date":"2021","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/34591994","citation_count":42,"is_preprint":false},{"pmid":"22402960","id":"PMC_22402960","title":"Exposure to bleomycin, etoposide, and cis-platinum alters rat sperm chromatin integrity and sperm head protein profile.","date":"2012","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/22402960","citation_count":39,"is_preprint":false},{"pmid":"8858345","id":"PMC_8858345","title":"Characterization of the 55-kb mouse histone gene cluster on chromosome 3.","date":"1996","source":"Genome research","url":"https://pubmed.ncbi.nlm.nih.gov/8858345","citation_count":37,"is_preprint":false},{"pmid":"2041781","id":"PMC_2041781","title":"Polyadenylated and 3' processed mRNAs are transcribed from the mouse histone H2A.X gene.","date":"1991","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/2041781","citation_count":36,"is_preprint":false},{"pmid":"12368243","id":"PMC_12368243","title":"Identification and confirmation of a module of coexpressed genes.","date":"2002","source":"Genome research","url":"https://pubmed.ncbi.nlm.nih.gov/12368243","citation_count":35,"is_preprint":false},{"pmid":"7948489","id":"PMC_7948489","title":"Separation of specific stages of spermatids from vitamin A-synchronized rat testes for assessment of nucleoprotein changes during spermiogenesis.","date":"1994","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/7948489","citation_count":35,"is_preprint":false},{"pmid":"12665578","id":"PMC_12665578","title":"The nonessential H2A N-terminal tail can function as an essential charge patch on the H2A.Z variant N-terminal tail.","date":"2003","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/12665578","citation_count":31,"is_preprint":false},{"pmid":"2038312","id":"PMC_2038312","title":"A common transcriptional activator is located in the coding region of two replication-dependent mouse histone genes.","date":"1991","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/2038312","citation_count":29,"is_preprint":false},{"pmid":"3025611","id":"PMC_3025611","title":"Characterization of two nonallelic pairs of late histone H2A and H2B genes of the sea urchin: differential regulation in the embryo and tissue-specific expression in the adult.","date":"1986","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/3025611","citation_count":29,"is_preprint":false},{"pmid":"6542967","id":"PMC_6542967","title":"Histone complements of human tissues, carcinomas, and carcinoma-derived cell lines.","date":"1984","source":"Molecular and cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/6542967","citation_count":24,"is_preprint":false},{"pmid":"16887128","id":"PMC_16887128","title":"Histone proteins determined in a human colon cancer by high-performance liquid chromatography and mass spectrometry.","date":"2006","source":"Journal of chromatography. A","url":"https://pubmed.ncbi.nlm.nih.gov/16887128","citation_count":24,"is_preprint":false},{"pmid":"20973679","id":"PMC_20973679","title":"Housekeeping gene transcript abundance in bovine fertilized and cloned embryos.","date":"2010","source":"Cellular reprogramming","url":"https://pubmed.ncbi.nlm.nih.gov/20973679","citation_count":22,"is_preprint":false},{"pmid":"21239733","id":"PMC_21239733","title":"Overexpression of histone variant H2A.1 and cellular transformation are related in N-nitrosodiethylamine-induced sequential hepatocarcinogenesis.","date":"2011","source":"Experimental biology and medicine (Maywood, N.J.)","url":"https://pubmed.ncbi.nlm.nih.gov/21239733","citation_count":21,"is_preprint":false},{"pmid":"8602367","id":"PMC_8602367","title":"Identification of a second conserved element within the coding sequence of a mouse H3 histone gene that interacts with nuclear factors and is necessary for normal expression.","date":"1996","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/8602367","citation_count":19,"is_preprint":false},{"pmid":"2425354","id":"PMC_2425354","title":"Drosophila histone H2A.2 is associated with the interbands of polytene chromosomes.","date":"1986","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/2425354","citation_count":15,"is_preprint":false},{"pmid":"24798243","id":"PMC_24798243","title":"New proteomic insights on the role of NPR-A in regulating self-renewal of embryonic stem cells.","date":"2014","source":"Stem cell reviews and reports","url":"https://pubmed.ncbi.nlm.nih.gov/24798243","citation_count":15,"is_preprint":false},{"pmid":"856814","id":"PMC_856814","title":"Immunological cross-reaction between calf and Drosophila histones.","date":"1977","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/856814","citation_count":15,"is_preprint":false},{"pmid":"21561626","id":"PMC_21561626","title":"Efficient organic monoliths prepared by γ-radiation induced polymerization in the evaluation of histone deacetylase inhibitors by capillary(nano)-high performance liquid chromatography and ion trap mass spectrometry.","date":"2011","source":"Journal of chromatography. A","url":"https://pubmed.ncbi.nlm.nih.gov/21561626","citation_count":15,"is_preprint":false},{"pmid":"34073722","id":"PMC_34073722","title":"A Circulating Exosome RNA Signature Is a Potential Diagnostic Marker for Pancreatic Cancer, a Systematic Study.","date":"2021","source":"Cancers","url":"https://pubmed.ncbi.nlm.nih.gov/34073722","citation_count":14,"is_preprint":false},{"pmid":"24764240","id":"PMC_24764240","title":"Expression of histone variant, H2A.1 is associated with the undifferentiated state of hepatocyte.","date":"2014","source":"Experimental biology and medicine (Maywood, N.J.)","url":"https://pubmed.ncbi.nlm.nih.gov/24764240","citation_count":13,"is_preprint":false},{"pmid":"2049400","id":"PMC_2049400","title":"Influence of chlorambucil, a bifunctional alkylating agent, on the histone variant biosynthesis of HEp-2 cells.","date":"1991","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/2049400","citation_count":13,"is_preprint":false},{"pmid":"31804179","id":"PMC_31804179","title":"Distinct roles for S. cerevisiae H2A copies in recombination and repeat stability, with a role for H2A.1 threonine 126.","date":"2019","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/31804179","citation_count":11,"is_preprint":false},{"pmid":"7240246","id":"PMC_7240246","title":"Immunological and organizational heterogeneity of histone H2a variants within chromatin of cells at different stages of Friend leukemia.","date":"1981","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/7240246","citation_count":11,"is_preprint":false},{"pmid":"8179821","id":"PMC_8179821","title":"The relative expression of human histone H2A genes is similar in different types of proliferating cells.","date":"1994","source":"DNA and cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/8179821","citation_count":11,"is_preprint":false},{"pmid":"14611817","id":"PMC_14611817","title":"Alterations in the expression and modification of histones in the liver after injury.","date":"2003","source":"Experimental and molecular pathology","url":"https://pubmed.ncbi.nlm.nih.gov/14611817","citation_count":10,"is_preprint":false},{"pmid":"2909389","id":"PMC_2909389","title":"Chromatin reorganization during emergence of malignant Friend tumors: early changes in H2A and H2B variants and nucleosome repeat length.","date":"1989","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/2909389","citation_count":10,"is_preprint":false},{"pmid":"3397394","id":"PMC_3397394","title":"The effects of in vitro age and culture state on histone variant synthesis in human diploid fibroblasts.","date":"1988","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/3397394","citation_count":6,"is_preprint":false},{"pmid":"8250883","id":"PMC_8250883","title":"A biochemical marker for differentiation is present in an in vitro aging cell system.","date":"1993","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/8250883","citation_count":6,"is_preprint":false},{"pmid":"28163185","id":"PMC_28163185","title":"Genomic characterization and dynamic methylation of promoter facilitates transcriptional regulation of H2A variants, H2A.1 and H2A.2 in various pathophysiological states of hepatocyte.","date":"2017","source":"The international journal of biochemistry & cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/28163185","citation_count":5,"is_preprint":false},{"pmid":"7397178","id":"PMC_7397178","title":"Nucleosome core protein: asymmetric dissociation of the octamer.","date":"1980","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/7397178","citation_count":5,"is_preprint":false},{"pmid":"3125994","id":"PMC_3125994","title":"Comparison of benzo[a]pyrene-diol-epoxide binding to histone H2A with different carboxy-terminal regions.","date":"1988","source":"Carcinogenesis","url":"https://pubmed.ncbi.nlm.nih.gov/3125994","citation_count":5,"is_preprint":false},{"pmid":"36447390","id":"PMC_36447390","title":"Human histone pre-mRNA assembles histone or canonical mRNA-processing complexes by overlapping 3'-end sequence elements.","date":"2022","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/36447390","citation_count":4,"is_preprint":false},{"pmid":"37414767","id":"PMC_37414767","title":"MOBILE pipeline enables identification of context-specific networks and regulatory mechanisms.","date":"2023","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/37414767","citation_count":4,"is_preprint":false},{"pmid":"8126082","id":"PMC_8126082","title":"Distribution of globin genes and histone variants in micrococcal nuclease-generated subfractions of chromatin from Friend erythroleukemia cells at different malignant states.","date":"1994","source":"Journal of cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8126082","citation_count":4,"is_preprint":false},{"pmid":"30970347","id":"PMC_30970347","title":"Genetic Polymorphisms Associated with Idiopathic Short Stature and First-Year Response to Growth Hormone Treatment.","date":"2019","source":"Hormone research in paediatrics","url":"https://pubmed.ncbi.nlm.nih.gov/30970347","citation_count":3,"is_preprint":false},{"pmid":"28352541","id":"PMC_28352541","title":"Incorporation of a tag helps to overcome expression variability in a recombinant host.","date":"2016","source":"Biotechnology reports (Amsterdam, Netherlands)","url":"https://pubmed.ncbi.nlm.nih.gov/28352541","citation_count":3,"is_preprint":false},{"pmid":"6975117","id":"PMC_6975117","title":"Histone variant composition of normal and leukaemic human lymphocytes: analysis by gel electrophoresis of whole cells and nuclei.","date":"1981","source":"British journal of haematology","url":"https://pubmed.ncbi.nlm.nih.gov/6975117","citation_count":3,"is_preprint":false},{"pmid":"41639907","id":"PMC_41639907","title":"Proteomic profiles in inclusion body myositis and polymyositis with mitochondrial pathology.","date":"2026","source":"Acta neuropathologica communications","url":"https://pubmed.ncbi.nlm.nih.gov/41639907","citation_count":1,"is_preprint":false},{"pmid":"37280829","id":"PMC_37280829","title":"ADP-Ribosylation of Histones in Nuclei Isolated from Embryos of the Sea Urchin, Hemicentrotus pulcherrimus: (histone/ADP-ribosylation/sea urchin/development/nucleus).","date":"1994","source":"Development, growth & differentiation","url":"https://pubmed.ncbi.nlm.nih.gov/37280829","citation_count":1,"is_preprint":false},{"pmid":"41020821","id":"PMC_41020821","title":"Histone-, Receptor-, and Integrin-Related Gene Products and ADAM28 as Relevant to B-Cell Acute Lymphoblastic Leukemia (B-ALL).","date":"2025","source":"Current issues in molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/41020821","citation_count":0,"is_preprint":false},{"pmid":"42036745","id":"PMC_42036745","title":"Cellular Senescence of Patient-derived Fibroblasts Reveals the Mid-old Stage as a Critical Window for Transcriptomic Signatures Linked to Alzheimer's Disease Biomarkers and Classification.","date":"2025","source":"Clinical psychopharmacology and neuroscience : the official scientific journal of the Korean College of Neuropsychopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/42036745","citation_count":0,"is_preprint":false},{"pmid":"7874752","id":"PMC_7874752","title":"Physical mapping of the Schizosaccharomyces pombe histone genes.","date":"1994","source":"Current genetics","url":"https://pubmed.ncbi.nlm.nih.gov/7874752","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":28330,"output_tokens":4348,"usd":0.075105,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12230,"output_tokens":3818,"usd":0.0783,"stage2_stop_reason":"end_turn"},"total_usd":0.153405,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1980,\n      \"finding\": \"The histone octamer (H3)2(H4)2(H2A)2(H2B)2 has a 2-fold axis of symmetry and forms a left-handed helical spool; the (H3)2(H4)2 tetramer forms the central turn while two H2A-H2B dimers lie on each face, each associated with approximately half a turn of DNA.\",\n      \"method\": \"Image reconstruction by electron microscopy to 22 Å resolution combined with cross-linking studies\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — structural reconstruction with functional model, foundational finding widely replicated\",\n      \"pmids\": [\"7422003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1980,\n      \"finding\": \"The nucleosomal core histone octamer dissociates asymmetrically: first releasing one H2A-H2B dimer to form a hexamer (H2A-H2B)-(H3)2-(H4)2, then releasing the second H2A-H2B dimer, leaving the (H3)2-(H4)2 tetramer. This dissociation is accelerated by increased temperature or decreased pH and is accompanied by conformational changes.\",\n      \"method\": \"Gel exclusion chromatography of isolated rat liver core histone octamer, monitored by histone composition and circular dichroism\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstitution assay, single lab, single study\",\n      \"pmids\": [\"7397178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1980,\n      \"finding\": \"H2A exists as at least eight protein species including H2A.1, H2A.2, H2A.X, and H2A.Z; all four variants are present in nucleosomal core particles; approximately 11% of each variant is conjugated to ubiquitin; the molar sum of all H2A species equals that of H4, H2B, or H3 in chromatin.\",\n      \"method\": \"SDS-PAGE, acetic acid-urea gels, nonionic detergent gels, isolation of nucleosomal core particles from mouse L1210 cells\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal gel systems, multiple cell/tissue types, foundational characterization replicated across labs\",\n      \"pmids\": [\"7407044\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1977,\n      \"finding\": \"H2A.2 and H2A.1 differ in primary structure (not post-synthetic modification of the same parent protein); H2A.2 contains a methionine critical to an antigenic difference that immunologically distinguishes it from H2A.1; antibodies against H2A.2 cross-react with H2A.1 but show higher specificity for H2A.2 at higher dilutions.\",\n      \"method\": \"Biochemical purification, amino acid analysis, immunological characterization with antibodies raised against purified H2A.2 subfraction\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical and immunological characterization using purified proteins, two orthogonal approaches\",\n      \"pmids\": [\"562183\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1981,\n      \"finding\": \"H2A.1 and H2A.2 have distinct organizational positions in chromatin: anti-H2A.1 IgG binds to intact chromatin and isolated nucleosomes, while anti-H2A.2 IgG does not bind, indicating that H2A.2-unique antigenic determinants are buried within the nucleosome core. H1-depleted, HMG-enriched nucleosomes react better with anti-H2A.1 than H1-containing nucleosomes.\",\n      \"method\": \"Radioimmunoassay using chromatin as immunoabsorbent and solid-phase binding of antibodies to nucleosome subfractions; antibodies directed against purified H2A.1 and H2A.2 variants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal antibody binding assay with chromatin and nucleosome subfractions, multiple cell types tested\",\n      \"pmids\": [\"7240246\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"H2A.1 and H2A.2 are synthesized and incorporated into chromatin at a significant rate even when DNA synthesis is inhibited, suggesting turnover of these histones independent of replication; H2A.1 has a higher turnover rate than H2A.2 in exponentially growing cells, a difference more pronounced in induced (differentiating) cells.\",\n      \"method\": \"Metabolic labeling with radioisotopes in murine erythroleukemia cells, pulse-chase analysis with DNA synthesis inhibitor, PAGE resolution of histone variants\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pulse-chase metabolic labeling with inhibitor controls, single lab\",\n      \"pmids\": [\"6593094\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"H2A.2 synthesized in G1 phase is deposited onto chromatin (old DNA) rather than selectively onto newly replicated DNA, unlike H3 and H4 which deposit primarily on newly replicated DNA in S phase. H2A.2 deposits to a 2–4-fold lower extent in G1 compared to H1 and HMGs.\",\n      \"method\": \"Cell synchronization in G1 and S phase, radiolabeling, chromatin fractionation to separate new and old DNA, PAGE\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell synchronization with radiolabeled pulse, DNA fractionation, single lab with multiple conditions\",\n      \"pmids\": [\"3935167\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"In Drosophila polytene chromosomes, H2A.2 localizes specifically to interbands (less compacted chromatin regions) as demonstrated by indirect immunofluorescence, whereas H2A.1 distributes throughout all chromosome regions, suggesting H2A.2 contributes to less compacted chromatin structure associated with gene-containing regions.\",\n      \"method\": \"Indirect immunofluorescence of polytene chromosomes using antibodies specific to H2A.1 and H2A.2\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization by immunofluorescence with variant-specific antibodies, tied to functional chromatin organization context\",\n      \"pmids\": [\"2425354\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"BPDE-I (benzo[a]pyrene diol-epoxide) binding to H2A.2 occurs primarily at the C-terminal octapeptide region; the C-terminal histidine residues present in rat and chicken H2A (including H2A.2) but absent in Xenopus H2A are the likely nucleophilic targets for BPDE-I adduct formation.\",\n      \"method\": \"HPLC analysis of BPDE-I-labeled core histones from nuclei, V8-protease digestion, carboxypeptidase B treatment of modified H2A.2, in vitro reaction of isolated C-terminal peptides with BPDE-I\",\n      \"journal\": \"Carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro peptide modification assay with enzymatic mapping, multiple species comparison, single lab\",\n      \"pmids\": [\"3125994\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"A coding region activating sequence (CRAS) in the H2a.2 gene (codons 50–85) is required for high-level expression; this element is orientation-dependent and position-independent; the same nuclear proteins interact with CRAS elements from both H2a.2 and H3.2 genes, indicating a common transcriptional regulatory factor for replication-dependent histone genes.\",\n      \"method\": \"In-frame deletion mutagenesis of H2a.2 coding region, stable transfection, gel mobility shift competition assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis + stable transfection + gel shift, single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"2038312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"H2A.1 and H2A.2 variants in rat spermatids undergo post-translational modification between steps 3 and 7 of spermiogenesis, as demonstrated by PAGE analysis showing altered electrophoretic mobility of both H2A variants at those stages.\",\n      \"method\": \"Vitamin A-synchronized rat testes, centrifugal elutriation to obtain spermatids at specific steps 1-12, PAGE analysis of basic nucleoproteins\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — PAGE-based detection of post-translational modification, single lab, modification type not identified\",\n      \"pmids\": [\"7948489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"H2A.2 is not ADP-ribosylated under normal conditions in sea urchin embryo nuclei at any developmental stage examined, but dimethylsulfate treatment induces poly-ADP-ribosylation of H2A.2 in embryos, indicating that ADP-ribosylation of H2A.2 is tightly regulated and suppressed during early development.\",\n      \"method\": \"2D-PAGE autoradiography of [32P]NAD+-labeled nuclei from sea urchin embryos, with and without dimethylsulfate treatment\",\n      \"journal\": \"Development, growth & differentiation\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single 2D-PAGE/autoradiography experiment in sea urchin (not mammalian), single lab\",\n      \"pmids\": [\"37280829\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Acetylation of the N-terminal tail of major H2A (H2A.1/H2A.2) in Tetrahymena is not essential for viability; however, the nonacetylatable N-terminal tail of major H2A can substitute for the essential acetylation function of the H2A.Z N-terminal tail, with the effects on viability determined by properties of the H2A core rather than the tail.\",\n      \"method\": \"In vitro mutagenesis of lysine residues + gene replacement in Tetrahymena thermophila, tail-swapping experiments between H2A.1/H2A.2 and H2A.Z\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — site-directed mutagenesis combined with in vivo gene replacement and tail-swap experiments, multiple orthogonal genetic tests\",\n      \"pmids\": [\"12665578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HIST2H2AA3 (H2AC18) mRNA is expressed as a polyadenylated mRNA in terminally differentiated fibroblasts but not in serum-starved fibroblasts, indicating that polyadenylated expression of this replication-dependent histone gene is part of the terminal differentiation program rather than a simple response to cell cycle arrest.\",\n      \"method\": \"RNA-seq and RT-PCR analysis of differentiated vs. serum-starved fibroblasts; conservation analysis across mammalian species\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNA-seq with RT-PCR validation in differentiated cells, single lab with multiple conditions and conservation analysis\",\n      \"pmids\": [\"27402160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"H2AC18 pre-mRNA can be processed by two mutually exclusive pathways: either by the replication-dependent histone machinery (producing non-polyadenylated mRNA ending at the stem-loop) or by the canonical polyadenylation machinery (producing polyadenylated mRNA). This dual processing capability arises because the canonical polyadenylation signal (AAUAAA) overlaps with the histone downstream element (HDE); disruption of the PAS sequence prevents recruitment of the canonical complex without affecting histone machinery recruitment.\",\n      \"method\": \"In vitro pre-mRNA processing assays with purified complexes, PAS mutagenesis, RNA-binding complex recruitment assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution of processing complexes, mutagenesis of cis-acting elements, mechanistic dissection with multiple orthogonal approaches in single rigorous study\",\n      \"pmids\": [\"36447390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In S. cerevisiae, CAG/CTG repeat stability depends on H2A.1 but not H2A.2; H2A.1 promotes high-fidelity homologous recombination, sister chromatid recombination, and break-induced replication through its unique Thr126 residue; hta1-T126A mutants are epistatic to deletion of Pol32 (Polδ subunit), placing H2A.1-Thr126 in the D-loop extension step of recombination. H2A.2 does not share these repair functions.\",\n      \"method\": \"Genetic analysis of CAG repeat stability in H2A copy mutants, epistasis analysis with pol32Δ, site-directed mutagenesis (T126A), sister chromatid recombination assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with mutagenesis in yeast, multiple repair assays, single lab; yeast H2A.2 ortholog context\",\n      \"pmids\": [\"31804179\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The H2A.2 (HIST2H2AA3) gene has a CpG island near its transcription start site; treatment with DNMT inhibitors increases H2A.2 expression while HDAC inhibitors also increase expression; methyl-DNA immunoprecipitation shows hyper-methylation of the H2A.2 promoter in embryonic and HCC tissue compared to control adult liver, indicating that DNA methylation dynamically regulates H2A.2 transcription across pathophysiological states.\",\n      \"method\": \"Transient transfection with dual luciferase reporter for cloned promoter sequences, DNMT/HDAC inhibitor treatment, methyl-DNA immunoprecipitation (MeDIP) coupled with qPCR, in silico CpG analysis\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — luciferase reporter + MeDIP + inhibitor experiments, multiple orthogonal approaches, single lab\",\n      \"pmids\": [\"28163185\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"H2AC18 (HIST2H2AA3/H2A.2) is a replication-dependent core histone that forms H2A-H2B dimers on each face of the (H3)2(H4)2 tetramer within the nucleosome octamer; its C-terminal histidine residues are sites of carcinogen (BPDE) adduct formation; its pre-mRNA undergoes mutually exclusive processing by either the histone stem-loop machinery or the canonical polyadenylation machinery through overlapping cis-elements; its expression in terminally differentiated cells occurs as polyadenylated mRNA as part of a differentiation program; and its promoter is subject to dynamic DNA methylation that regulates variant-specific transcription across proliferative and differentiation states.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"H2AC18 (HIST2H2AA3/H2A.2) is a replication-dependent core histone of the H2A family that assembles into the nucleosome as part of an H2A-H2B dimer; two such dimers lie on each face of the (H3)2(H4)2 tetramer to complete the octamer that wraps DNA into the chromatin fiber [#0, #2]. H2A.2 is a distinct primary-sequence variant rather than a modified form of H2A.1, carrying variant-specific antigenic determinants and a critical methionine that immunologically distinguish it [#3]; its unique determinants are buried within the nucleosome core, indicating a distinct organizational position relative to H2A.1 [#4]. Functionally, the two variants are non-equivalent: H2A.2 turns over more slowly than H2A.1, deposits onto bulk (old) DNA rather than selectively onto newly replicated DNA, and preferentially associates with less compacted, gene-containing interband chromatin [#5, #6, #7]. The C-terminal histidine residues of H2A.2 are the principal nucleophilic targets for adduct formation by the carcinogen BPDE [#8]. High-level transcription depends on a coding-region activating sequence (CRAS) bound by a factor shared with other replication-dependent histone genes [#9], and the gene's promoter CpG island is subject to dynamic DNA methylation that modulates variant-specific expression across proliferative, embryonic, and hepatocellular carcinoma states [#16]. Although replication-dependent, H2AC18 pre-mRNA can be processed by two mutually exclusive routes—the histone stem-loop machinery or the canonical polyadenylation machinery—because the polyadenylation signal overlaps the histone downstream element; polyadenylated expression occurs as part of a terminal differentiation program [#13, #14].\",\n  \"teleology\": [\n    {\n      \"year\": 1980,\n      \"claim\": \"Established the structural context in which H2A functions, showing how H2A-H2B dimers assemble onto the (H3)2(H4)2 tetramer to build the nucleosome and organize DNA.\",\n      \"evidence\": \"EM image reconstruction to 22 Å plus cross-linking of the histone octamer; gel-exclusion chromatography of isolated octamers monitored by CD\",\n      \"pmids\": [\"7422003\", \"7397178\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not resolve variant-specific positioning of H2A.2 within the octamer\", \"In vitro dissociation behavior not linked to a specific H2A variant\"]\n    },\n    {\n      \"year\": 1980,\n      \"claim\": \"Defined H2A as a family of distinct protein species present together in core particles, framing the question of what distinguishes individual variants such as H2A.2.\",\n      \"evidence\": \"Multiple orthogonal gel systems on nucleosomal core particles from mouse L1210 cells\",\n      \"pmids\": [\"7407044\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not assign function to individual variants\", \"Ubiquitin-conjugation fraction not mapped to specific variants\"]\n    },\n    {\n      \"year\": 1977,\n      \"claim\": \"Demonstrated that H2A.2 is a genuine primary-sequence variant of H2A.1, not a post-synthetically modified form, with a unique methionine producing an antigenic difference.\",\n      \"evidence\": \"Biochemical purification, amino acid analysis, and immunological characterization with variant-specific antibodies\",\n      \"pmids\": [\"562183\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Antibody cross-reactivity limits absolute specificity\", \"Functional consequence of the sequence difference not addressed\"]\n    },\n    {\n      \"year\": 1981,\n      \"claim\": \"Showed that H2A.2 occupies a distinct organizational position in chromatin, its unique determinants buried within the nucleosome core unlike those of H2A.1.\",\n      \"evidence\": \"Reciprocal radioimmunoassay using chromatin and nucleosome subfractions with variant-specific antibodies\",\n      \"pmids\": [\"7240246\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of differential burial not defined\", \"No direct structural assignment of H2A.2 placement\"]\n    },\n    {\n      \"year\": 1984,\n      \"claim\": \"Revealed that H2A.2 has replication-independent turnover with kinetics distinct from H2A.1, more pronounced in differentiating cells, linking the variant to chromatin dynamics beyond S phase.\",\n      \"evidence\": \"Metabolic pulse-chase labeling with a DNA synthesis inhibitor in murine erythroleukemia cells\",\n      \"pmids\": [\"6593094\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of replication-independent deposition not identified\", \"Single cell system\"]\n    },\n    {\n      \"year\": 1985,\n      \"claim\": \"Showed that G1-synthesized H2A.2 deposits onto pre-existing (old) DNA rather than newly replicated DNA, distinguishing its deposition behavior from H3 and H4.\",\n      \"evidence\": \"Cell synchronization, radiolabeling, and chromatin fractionation separating new and old DNA\",\n      \"pmids\": [\"3935167\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Chaperone/deposition machinery for H2A.2 not identified\", \"Functional consequence of old-DNA deposition unresolved\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"Linked H2A.2 to chromatin architecture by showing its preferential localization to less-compacted, gene-containing interband regions, unlike the ubiquitous H2A.1.\",\n      \"evidence\": \"Indirect immunofluorescence of Drosophila polytene chromosomes with variant-specific antibodies\",\n      \"pmids\": [\"2425354\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal role in decompaction versus correlation not established\", \"Drosophila context may not map directly to mammalian H2AC18\"]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"Identified the C-terminal histidine residues of H2A.2 as the nucleophilic targets of the carcinogen BPDE, implicating the variant in carcinogen-DNA/protein adduct chemistry.\",\n      \"evidence\": \"HPLC, V8/carboxypeptidase mapping of BPDE-labeled histones, and in vitro peptide reactions across species\",\n      \"pmids\": [\"3125994\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Biological consequence of adduct formation not determined\", \"Single lab\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Defined a coding-region activating sequence (CRAS) required for high-level H2a.2 transcription and bound by a factor shared with other replication-dependent histone genes, identifying a common regulatory mechanism.\",\n      \"evidence\": \"In-frame coding deletion mutagenesis, stable transfection, and gel mobility-shift competition assays\",\n      \"pmids\": [\"2038312\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the CRAS-binding factor not established\", \"Mechanism of orientation-dependence unresolved\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Tested the essentiality of major-H2A N-terminal acetylation, showing it is dispensable for viability and that the core, not the tail, dictates functional substitution for H2A.Z.\",\n      \"evidence\": \"Lysine mutagenesis, gene replacement, and tail-swap experiments in Tetrahymena\",\n      \"pmids\": [\"12665578\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not separate H2A.1 from H2A.2 contributions\", \"Tetrahymena context\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed that polyadenylated expression of this replication-dependent histone gene is a feature of the terminal differentiation program rather than mere cell-cycle arrest.\",\n      \"evidence\": \"RNA-seq and RT-PCR in differentiated versus serum-starved fibroblasts with cross-mammalian conservation analysis\",\n      \"pmids\": [\"27402160\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role of the polyadenylated isoform not defined\", \"Trans-factors driving the switch unidentified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated that promoter CpG-island DNA methylation dynamically regulates H2A.2 transcription across embryonic, adult, and hepatocellular carcinoma states.\",\n      \"evidence\": \"Dual-luciferase promoter reporters, DNMT/HDAC inhibitor treatment, and MeDIP-qPCR\",\n      \"pmids\": [\"28163185\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal contribution to tumorigenesis not established\", \"Methylation-sensitive transcription factors unidentified\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Resolved how a single pre-mRNA can yield either histone-type or polyadenylated transcripts, showing the canonical PAS overlaps the histone downstream element so the two processing routes are mutually exclusive.\",\n      \"evidence\": \"In vitro processing assays with purified complexes, PAS mutagenesis, and complex-recruitment assays\",\n      \"pmids\": [\"36447390\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo determinants of pathway choice not defined\", \"Regulatory signals selecting between machineries unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How H2A.2's distinct deposition, turnover, and chromatin localization translate into a specific genomic function, and what selects its dual pre-mRNA processing fate in vivo, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No deposition chaperone identified for H2AC18\", \"Genome-wide occupancy of the variant in mammalian cells not mapped\", \"In vivo trigger for polyadenylated versus stem-loop processing unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [0, 4, 7]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [0, 7]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [14]}\n    ],\n    \"complexes\": [\"nucleosome\"],\n    \"partners\": [\"H2B\", \"H3\", \"H4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}