{"gene":"PF3D7_0714000","run_date":"2026-09-08T12:51:27","timeline":{"discoveries":[{"year":2013,"finding":"H2B.Z (PF3D7_0714000) dimerizes with the H2A variant H2A.Z within nucleosomes, forming double-variant nucleosomes. These H2A.Z/H2B.Z nucleosomes are enriched in intergenic (euchromatic) regions genome-wide and specifically occupy the promoter of the single active var gene copy, with this enrichment being developmentally regulated across the intraerythrocytic cycle.","method":"ChIP-seq combined with correlation analysis of H2A.Z and H2B.Z occupancy across the genome; developmental stage comparisons","journal":"Molecular microbiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — two independent labs (PMID:23373537 and PMID:23320541) used ChIP-seq with orthogonal approaches and reached concordant conclusions about H2A.Z/H2B.Z double-variant nucleosome formation and genomic distribution","pmids":["23373537","23320541"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2013,"finding":"H2B.Z (PF3D7_0714000) occupancy localizes specifically to euchromatic intergenic regions throughout intraerythrocytic development, is enriched in promoters over 3′ intergenic regions, and its occupancy correlates with promoter strength but not with temporal (stage-specific) promoter activity. H2B.Z occupancy also exhibits a clear correlation with the AT-content of the underlying DNA sequence.","method":"Genome-wide ChIP-seq during intraerythrocytic development with analysis of promoter vs. coding vs. 3′ intergenic region enrichment and correlation with DNA base composition","journal":"Molecular microbiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide ChIP-seq with multiple analytical axes (promoter strength, temporal activity, AT-content), independently replicated by a second lab in the same year","pmids":["23320541"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"finding":"Mass spectrometry analysis of acid-extracted P. falciparum histones revealed a distinct post-translational modification pattern for H2B.Z (PF3D7_0714000) compared to canonical H2B, suggesting divergent functions of the two H2B variants in the parasite.","method":"LC-MS/MS proteomics of acid-extracted histones using Q-TOF and LTQ-FT mass spectrometry; peptide-level PTM mapping","journal":"Journal of proteome research","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — high-quality mass spectrometry with high mass accuracy, but single-lab study with no functional follow-up reported in the abstract","pmids":["19351122"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2023,"finding":"PfSir2 histone deacetylases antagonize acetylated H2B.Z (PF3D7_0714000) at the boundaries between active and silent DNA (heterochromatin boundaries), implicating acetylated H2B.Z in the mechanism regulating P. falciparum variant gene silencing. Additionally, acetylation of H2B.Z at promoters is dynamically associated with promoter activity across the genome.","method":"ChIP-seq profiling of acetylated alternative histones combined with PfSir2 loss-of-function analysis; genome-wide occupancy correlation with promoter activity","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP-seq with genetic perturbation (PfSir2), two orthogonal readouts (heterochromatin boundaries and promoter activity), single lab","pmids":["37882786"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2023,"finding":"In female gametocytes, H2B.Z (PF3D7_0714000) together with H2A.Z becomes highly enriched in H3K9me3-associated heterochromatin, representing a sex-specific chromatin state distinct from that observed in asexual parasites where H2A.Z/H2B.Z double-variant nucleosomes mark euchromatic intergenic regions.","method":"Flow cytometry separation of male and female gametocytes followed by ChIP-seq profiling of H2B.Z, H2A.Z, and H3K9me3","journal":"BMC biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP-seq with sex-sorted cells and multiple histone marks profiled, single lab","pmids":["37013531"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"finding":"PfGCN5 (via its bromodomain, BRD) is required for acetylation of H2B.Z (PF3D7_0714000) at euchromatic gene promoters. Loss of the PfGCN5 BRD reduced H2B.Z acetylation at promoters and simultaneously increased levels of acetylated H2B.Z in heterochromatin, de-repressing heterochromatic genes. The BRD-binding compound L-45 phenocopied BRD deletion, implicating PfGCN5 as the acetyltransferase or BRD-dependent recruiter responsible for H2B.Z acetylation status.","method":"Conditional deletion/mutation of PfGCN5 bromodomain; ChIP-seq of acetylated H2B.Z in wild-type vs. BRD-deleted parasites; pharmacological inhibition with compound L-45; transcriptome analysis","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic perturbation of a specific domain combined with ChIP-seq of H2B.Z acetylation and pharmacological phenocopy, multiple orthogonal methods in a single study","pmids":["40156869"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"finding":"H2B.Z (PF3D7_0714000) together with H2A.Z was found associated with the PfSWR1 chromatin remodeling complex by reciprocal pulldown, indicating that PfSWR1 is the complex responsible for depositing the H2A.Z/H2B.Z variant histone pair into nucleosomes at activated promoters.","method":"Reciprocal co-immunoprecipitation/pulldown using tagged PfEAF2 followed by mass spectrometry identification of associated proteins","journal":"mSphere","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal pulldown with mass spectrometry identification, but H2B.Z association is reported as part of a broader complex study with limited H2B.Z-specific functional follow-up","pmids":["38564734"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2006,"finding":"H2B.Z (PF3D7_0714000, referred to as H2Bv in this study) was identified as a variant histone encoded by the P. falciparum genome, and mass spectrometry confirmed its synthesis in blood-stage parasites. Expression of this variant histone decreased in mid- or late trophozoite stages, in contrast to core histones that increase during late trophozoite stage.","method":"Mass spectrometry confirmation of protein synthesis; real-time RT-PCR and immunoblotting for stage-specific expression","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mass spectrometry plus RT-PCR and immunoblotting provide orthogonal confirmation of expression and synthesis, single lab","pmids":["16410041"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"H2B.Z (PF3D7_0714000) is an apicomplexan-specific histone variant that forms double-variant nucleosomes by dimerizing with H2A.Z; these nucleosomes are deposited by the PfSWR1 complex and mark euchromatic intergenic regions and active promoters genome-wide, with occupancy correlated with promoter strength and AT-rich DNA content, while PfGCN5 (via its bromodomain) is required for H2B.Z acetylation at promoters and for maintaining repressive heterochromatin; PfSir2 deacetylases antagonize acetylated H2B.Z at heterochromatin boundaries to enforce variant gene silencing, and in female gametocytes H2B.Z undergoes a sex-specific redistribution into H3K9me3-marked heterochromatin."},"narrative":{"mechanistic_narrative":"H2B.Z (PF3D7_0714000) is an apicomplexan-specific histone H2B variant of Plasmodium falciparum that partitions the parasite genome into active and silent chromatin states across development [PMID:23373537, PMID:23320541]. It was first identified as a genome-encoded variant histone whose synthesis is confirmed in blood-stage parasites and declines in mid-to-late trophozoites, opposite to core histones [PMID:16410041]. Mechanistically, H2B.Z dimerizes with the H2A variant H2A.Z to form double-variant nucleosomes that are enriched in euchromatic intergenic regions genome-wide and specifically occupy the promoter of the active var gene copy [PMID:23373537, PMID:23320541]; occupancy is concentrated at promoters over 3′ intergenic regions, tracks with promoter strength and with underlying AT-content, but not with stage-specific promoter timing [PMID:23320541]. These variant nucleosomes are deposited by the PfSWR1 chromatin remodeling complex, with which H2B.Z and H2A.Z co-purify by reciprocal pulldown [PMID:38564734]. Acetylation of H2B.Z is the regulatory switch on this system: PfGCN5, through its bromodomain, is required for H2B.Z acetylation at euchromatic promoters, and loss of the bromodomain redistributes acetylated H2B.Z into heterochromatin and de-represses heterochromatic genes [PMID:40156869], while PfSir2 deacetylases antagonize acetylated H2B.Z at heterochromatin boundaries to enforce variant gene silencing [PMID:37882786]. In female gametocytes, H2B.Z together with H2A.Z is redistributed into H3K9me3-associated heterochromatin, defining a sex-specific chromatin state distinct from the euchromatic asexual pattern [PMID:37013531].","teleology":[{"year":2006,"claim":"Establishing that P. falciparum encodes and actually synthesizes a distinct H2B variant was the entry point for treating H2B.Z as a functional chromatin component rather than a genome annotation.","evidence":"mass spectrometry confirmation of protein synthesis plus RT-PCR and immunoblotting for stage-specific expression in blood-stage parasites","pmids":["16410041"],"confidence":"Medium","gaps":["No genomic localization or nucleosome context defined","Functional role in transcription untested"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"claim":"Showing that H2B.Z carries a post-translational modification pattern distinct from canonical H2B raised the hypothesis that the variant has functions divergent from the core histone.","evidence":"LC-MS/MS proteomics of acid-extracted histones with peptide-level PTM mapping","pmids":["19351122"],"confidence":"Medium","gaps":["Specific modified residues and their function not resolved","No enzyme assigned to the modifications","Single-lab, no functional follow-up"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2013,"claim":"Defining that H2B.Z pairs with H2A.Z in double-variant nucleosomes and maps to euchromatic promoters answered where and in what molecular form the variant acts, linking it to active gene expression and the active var promoter.","evidence":"ChIP-seq of H2A.Z and H2B.Z occupancy with correlation analysis, promoter/coding/3′ partitioning, AT-content and promoter-strength correlations, across intraerythrocytic development; concordant results from two independent labs","pmids":["23373537","23320541"],"confidence":"High","gaps":["Mechanism of targeting to promoters and AT-rich DNA not defined","Deposition machinery unidentified","Causality between occupancy and transcription untested"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2023,"claim":"Identifying acetylated H2B.Z as a target antagonized by PfSir2 at heterochromatin boundaries connected the variant's acetylation state to the enforcement of variant gene silencing.","evidence":"ChIP-seq of acetylated alternative histones with PfSir2 loss-of-function and promoter-activity correlation","pmids":["37882786"],"confidence":"Medium","gaps":["Acetyltransferase responsible not yet identified in this study","Direct versus indirect PfSir2 action on H2B.Z not resolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2023,"claim":"Sex-sorted profiling revealed that H2B.Z relocates with H2A.Z into H3K9me3 heterochromatin in female gametocytes, establishing that the variant's chromatin role is developmentally reprogrammed rather than fixed.","evidence":"flow-cytometry separation of male and female gametocytes followed by ChIP-seq of H2B.Z, H2A.Z, and H3K9me3","pmids":["37013531"],"confidence":"Medium","gaps":["Trigger and machinery of the sex-specific redistribution unknown","Functional consequence for gametocyte gene expression not established"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"claim":"Reciprocal pulldown placing H2B.Z and H2A.Z with PfSWR1 identified the deposition machinery that installs the variant pair, filling the mechanistic gap left by the localization studies.","evidence":"reciprocal co-immunoprecipitation with tagged PfEAF2 and mass spectrometry identification of associated proteins","pmids":["38564734"],"confidence":"Medium","gaps":["H2B.Z-specific functional consequence of PfSWR1 loss not tested here","How PfSWR1 selects target promoters unresolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"claim":"Demonstrating that PfGCN5 via its bromodomain controls H2B.Z acetylation and its euchromatin-versus-heterochromatin partitioning identified the enzyme/recruiter governing the acetylation switch and connected it to heterochromatic gene repression.","evidence":"conditional deletion of the PfGCN5 bromodomain with ChIP-seq of acetylated H2B.Z, pharmacological phenocopy with compound L-45, and transcriptome analysis","pmids":["40156869"],"confidence":"High","gaps":["Whether PfGCN5 directly acetylates H2B.Z or acts as a BRD-dependent recruiter not fully distinguished","Specific acetylated residues on H2B.Z not mapped in this study"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"How H2B.Z occupancy and acetylation state are causally translated into transcriptional output, and what molecular signal drives its developmental redistribution between euchromatin and heterochromatin, remain open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No direct loss-of-function of H2B.Z itself linking variant deposition to gene expression in the corpus","Structural basis of H2A.Z/H2B.Z double-variant nucleosome not characterized","Signals directing the female-gametocyte heterochromatin switch unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["PfSWR1 chromatin remodeling complex (H2B.Z/H2A.Z associated via reciprocal pulldown) [#6]","H2A.Z/H2B.Z double-variant nucleosome [#0]"],"partners":["H2A.Z (DIMERIZATION PARTNER IN DOUBLE-VARIANT NUCLEOSOMES) [#0, #4]","PFSWR1 / PFEAF2 (DEPOSITION COMPLEX) [#6]","PFGCN5 BROMODOMAIN (ACETYLATION OF H2B.Z) [#5]","PFSIR2 (DEACETYLASE ANTAGONIZING ACETYLATED H2B.Z) [#3]"],"other_free_text":["H2B.Z occupancy correlates with promoter strength and AT-content but not stage-specific promoter timing [#1]","Acetylation state of H2B.Z governs its euchromatin-versus-heterochromatin partitioning and variant gene silencing [#3, #5]","Female-gametocyte-specific redistribution of H2B.Z into H3K9me3 heterochromatin [#4]","Variant expression declines in mid/late trophozoites, opposite to core histones [#7]","Distinct PTM pattern relative to canonical H2B [#2]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"16410041","id":"PMC_16410041","title":"The malaria parasite Plasmodium falciparum histones: organization, expression, and acetylation.","date":"2006","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/16410041","citation_count":155,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["curated_ref"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"19351122","id":"PMC_19351122","title":"Global histone analysis by mass spectrometry reveals a high content of acetylated lysine residues in the malaria parasite Plasmodium falciparum.","date":"2009","source":"Journal of proteome 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parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/10579431","citation_count":10,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["H2B"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"37882786","id":"PMC_37882786","title":"The P. falciparum alternative histones Pf H2A.Z and Pf H2B.Z are dynamically acetylated and antagonized by PfSir2 histone deacetylases at heterochromatin boundaries.","date":"2023","source":"mBio","url":"https://pubmed.ncbi.nlm.nih.gov/37882786","citation_count":8,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["H2B.Z","H2B"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"12739134","id":"PMC_12739134","title":"The histone H4 gene of Plasmodium falciparum is developmentally transcribed in asexual parasites.","date":"2003","source":"Parasitology 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These H2A.Z/H2B.Z nucleosomes are enriched in intergenic (euchromatic) regions genome-wide and specifically occupy the promoter of the single active var gene copy, with this enrichment being developmentally regulated across the intraerythrocytic cycle.\",\n      \"method\": \"ChIP-seq combined with correlation analysis of H2A.Z and H2B.Z occupancy across the genome; developmental stage comparisons\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two independent labs (PMID:23373537 and PMID:23320541) used ChIP-seq with orthogonal approaches and reached concordant conclusions about H2A.Z/H2B.Z double-variant nucleosome formation and genomic distribution\",\n      \"pmids\": [\"23373537\", \"23320541\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"H2B.Z (PF3D7_0714000) occupancy localizes specifically to euchromatic intergenic regions throughout intraerythrocytic development, is enriched in promoters over 3′ intergenic regions, and its occupancy correlates with promoter strength but not with temporal (stage-specific) promoter activity. H2B.Z occupancy also exhibits a clear correlation with the AT-content of the underlying DNA sequence.\",\n      \"method\": \"Genome-wide ChIP-seq during intraerythrocytic development with analysis of promoter vs. coding vs. 3′ intergenic region enrichment and correlation with DNA base composition\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide ChIP-seq with multiple analytical axes (promoter strength, temporal activity, AT-content), independently replicated by a second lab in the same year\",\n      \"pmids\": [\"23320541\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Mass spectrometry analysis of acid-extracted P. falciparum histones revealed a distinct post-translational modification pattern for H2B.Z (PF3D7_0714000) compared to canonical H2B, suggesting divergent functions of the two H2B variants in the parasite.\",\n      \"method\": \"LC-MS/MS proteomics of acid-extracted histones using Q-TOF and LTQ-FT mass spectrometry; peptide-level PTM mapping\",\n      \"journal\": \"Journal of proteome research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — high-quality mass spectrometry with high mass accuracy, but single-lab study with no functional follow-up reported in the abstract\",\n      \"pmids\": [\"19351122\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PfSir2 histone deacetylases antagonize acetylated H2B.Z (PF3D7_0714000) at the boundaries between active and silent DNA (heterochromatin boundaries), implicating acetylated H2B.Z in the mechanism regulating P. falciparum variant gene silencing. Additionally, acetylation of H2B.Z at promoters is dynamically associated with promoter activity across the genome.\",\n      \"method\": \"ChIP-seq profiling of acetylated alternative histones combined with PfSir2 loss-of-function analysis; genome-wide occupancy correlation with promoter activity\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP-seq with genetic perturbation (PfSir2), two orthogonal readouts (heterochromatin boundaries and promoter activity), single lab\",\n      \"pmids\": [\"37882786\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In female gametocytes, H2B.Z (PF3D7_0714000) together with H2A.Z becomes highly enriched in H3K9me3-associated heterochromatin, representing a sex-specific chromatin state distinct from that observed in asexual parasites where H2A.Z/H2B.Z double-variant nucleosomes mark euchromatic intergenic regions.\",\n      \"method\": \"Flow cytometry separation of male and female gametocytes followed by ChIP-seq profiling of H2B.Z, H2A.Z, and H3K9me3\",\n      \"journal\": \"BMC biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP-seq with sex-sorted cells and multiple histone marks profiled, single lab\",\n      \"pmids\": [\"37013531\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PfGCN5 (via its bromodomain, BRD) is required for acetylation of H2B.Z (PF3D7_0714000) at euchromatic gene promoters. Loss of the PfGCN5 BRD reduced H2B.Z acetylation at promoters and simultaneously increased levels of acetylated H2B.Z in heterochromatin, de-repressing heterochromatic genes. The BRD-binding compound L-45 phenocopied BRD deletion, implicating PfGCN5 as the acetyltransferase or BRD-dependent recruiter responsible for H2B.Z acetylation status.\",\n      \"method\": \"Conditional deletion/mutation of PfGCN5 bromodomain; ChIP-seq of acetylated H2B.Z in wild-type vs. BRD-deleted parasites; pharmacological inhibition with compound L-45; transcriptome analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic perturbation of a specific domain combined with ChIP-seq of H2B.Z acetylation and pharmacological phenocopy, multiple orthogonal methods in a single study\",\n      \"pmids\": [\"40156869\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"H2B.Z (PF3D7_0714000) together with H2A.Z was found associated with the PfSWR1 chromatin remodeling complex by reciprocal pulldown, indicating that PfSWR1 is the complex responsible for depositing the H2A.Z/H2B.Z variant histone pair into nucleosomes at activated promoters.\",\n      \"method\": \"Reciprocal co-immunoprecipitation/pulldown using tagged PfEAF2 followed by mass spectrometry identification of associated proteins\",\n      \"journal\": \"mSphere\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal pulldown with mass spectrometry identification, but H2B.Z association is reported as part of a broader complex study with limited H2B.Z-specific functional follow-up\",\n      \"pmids\": [\"38564734\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"H2B.Z (PF3D7_0714000, referred to as H2Bv in this study) was identified as a variant histone encoded by the P. falciparum genome, and mass spectrometry confirmed its synthesis in blood-stage parasites. Expression of this variant histone decreased in mid- or late trophozoite stages, in contrast to core histones that increase during late trophozoite stage.\",\n      \"method\": \"Mass spectrometry confirmation of protein synthesis; real-time RT-PCR and immunoblotting for stage-specific expression\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mass spectrometry plus RT-PCR and immunoblotting provide orthogonal confirmation of expression and synthesis, single lab\",\n      \"pmids\": [\"16410041\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"H2B.Z (PF3D7_0714000) is an apicomplexan-specific histone variant that forms double-variant nucleosomes by dimerizing with H2A.Z; these nucleosomes are deposited by the PfSWR1 complex and mark euchromatic intergenic regions and active promoters genome-wide, with occupancy correlated with promoter strength and AT-rich DNA content, while PfGCN5 (via its bromodomain) is required for H2B.Z acetylation at promoters and for maintaining repressive heterochromatin; PfSir2 deacetylases antagonize acetylated H2B.Z at heterochromatin boundaries to enforce variant gene silencing, and in female gametocytes H2B.Z undergoes a sex-specific redistribution into H3K9me3-marked heterochromatin.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"H2B.Z (PF3D7_0714000) is an apicomplexan-specific histone H2B variant of Plasmodium falciparum that partitions the parasite genome into active and silent chromatin states across development [#0, #1]. It was first identified as a genome-encoded variant histone whose synthesis is confirmed in blood-stage parasites and declines in mid-to-late trophozoites, opposite to core histones [#7]. Mechanistically, H2B.Z dimerizes with the H2A variant H2A.Z to form double-variant nucleosomes that are enriched in euchromatic intergenic regions genome-wide and specifically occupy the promoter of the active var gene copy [#0]; occupancy is concentrated at promoters over 3\\u2032 intergenic regions, tracks with promoter strength and with underlying AT-content, but not with stage-specific promoter timing [#1]. These variant nucleosomes are deposited by the PfSWR1 chromatin remodeling complex, with which H2B.Z and H2A.Z co-purify by reciprocal pulldown [#6]. Acetylation of H2B.Z is the regulatory switch on this system: PfGCN5, through its bromodomain, is required for H2B.Z acetylation at euchromatic promoters, and loss of the bromodomain redistributes acetylated H2B.Z into heterochromatin and de-represses heterochromatic genes [#5], while PfSir2 deacetylases antagonize acetylated H2B.Z at heterochromatin boundaries to enforce variant gene silencing [#3]. In female gametocytes, H2B.Z together with H2A.Z is redistributed into H3K9me3-associated heterochromatin, defining a sex-specific chromatin state distinct from the euchromatic asexual pattern [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Establishing that P. falciparum encodes and actually synthesizes a distinct H2B variant was the entry point for treating H2B.Z as a functional chromatin component rather than a genome annotation.\",\n      \"evidence\": \"mass spectrometry confirmation of protein synthesis plus RT-PCR and immunoblotting for stage-specific expression in blood-stage parasites\",\n      \"pmids\": [\"16410041\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No genomic localization or nucleosome context defined\", \"Functional role in transcription untested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Showing that H2B.Z carries a post-translational modification pattern distinct from canonical H2B raised the hypothesis that the variant has functions divergent from the core histone.\",\n      \"evidence\": \"LC-MS/MS proteomics of acid-extracted histones with peptide-level PTM mapping\",\n      \"pmids\": [\"19351122\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific modified residues and their function not resolved\", \"No enzyme assigned to the modifications\", \"Single-lab, no functional follow-up\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Defining that H2B.Z pairs with H2A.Z in double-variant nucleosomes and maps to euchromatic promoters answered where and in what molecular form the variant acts, linking it to active gene expression and the active var promoter.\",\n      \"evidence\": \"ChIP-seq of H2A.Z and H2B.Z occupancy with correlation analysis, promoter/coding/3\\u2032 partitioning, AT-content and promoter-strength correlations, across intraerythrocytic development; concordant results from two independent labs\",\n      \"pmids\": [\"23373537\", \"23320541\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of targeting to promoters and AT-rich DNA not defined\", \"Deposition machinery unidentified\", \"Causality between occupancy and transcription untested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identifying acetylated H2B.Z as a target antagonized by PfSir2 at heterochromatin boundaries connected the variant's acetylation state to the enforcement of variant gene silencing.\",\n      \"evidence\": \"ChIP-seq of acetylated alternative histones with PfSir2 loss-of-function and promoter-activity correlation\",\n      \"pmids\": [\"37882786\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Acetyltransferase responsible not yet identified in this study\", \"Direct versus indirect PfSir2 action on H2B.Z not resolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Sex-sorted profiling revealed that H2B.Z relocates with H2A.Z into H3K9me3 heterochromatin in female gametocytes, establishing that the variant's chromatin role is developmentally reprogrammed rather than fixed.\",\n      \"evidence\": \"flow-cytometry separation of male and female gametocytes followed by ChIP-seq of H2B.Z, H2A.Z, and H3K9me3\",\n      \"pmids\": [\"37013531\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Trigger and machinery of the sex-specific redistribution unknown\", \"Functional consequence for gametocyte gene expression not established\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Reciprocal pulldown placing H2B.Z and H2A.Z with PfSWR1 identified the deposition machinery that installs the variant pair, filling the mechanistic gap left by the localization studies.\",\n      \"evidence\": \"reciprocal co-immunoprecipitation with tagged PfEAF2 and mass spectrometry identification of associated proteins\",\n      \"pmids\": [\"38564734\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"H2B.Z-specific functional consequence of PfSWR1 loss not tested here\", \"How PfSWR1 selects target promoters unresolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrating that PfGCN5 via its bromodomain controls H2B.Z acetylation and its euchromatin-versus-heterochromatin partitioning identified the enzyme/recruiter governing the acetylation switch and connected it to heterochromatic gene repression.\",\n      \"evidence\": \"conditional deletion of the PfGCN5 bromodomain with ChIP-seq of acetylated H2B.Z, pharmacological phenocopy with compound L-45, and transcriptome analysis\",\n      \"pmids\": [\"40156869\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PfGCN5 directly acetylates H2B.Z or acts as a BRD-dependent recruiter not fully distinguished\", \"Specific acetylated residues on H2B.Z not mapped in this study\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How H2B.Z occupancy and acetylation state are causally translated into transcriptional output, and what molecular signal drives its developmental redistribution between euchromatin and heterochromatin, remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct loss-of-function of H2B.Z itself linking variant deposition to gene expression in the corpus\", \"Structural basis of H2A.Z/H2B.Z double-variant nucleosome not characterized\", \"Signals directing the female-gametocyte heterochromatin switch unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0046982\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0000786\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"GO:0000790\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0000792\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0006355\", \"supporting_discovery_ids\": [1, 3, 5]},\n      {\"term_id\": \"GO:0006338\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0016575\", \"supporting_discovery_ids\": [3, 5]}\n    ],\n    \"complexes\": [\n      \"PfSWR1 chromatin remodeling complex (H2B.Z/H2A.Z associated via reciprocal pulldown) [#6]\",\n      \"H2A.Z/H2B.Z double-variant nucleosome [#0]\"\n    ],\n    \"partners\": [\n      \"H2A.Z (dimerization partner in double-variant nucleosomes) [#0, #4]\",\n      \"PfSWR1 / PfEAF2 (deposition complex) [#6]\",\n      \"PfGCN5 bromodomain (acetylation of H2B.Z) [#5]\",\n      \"PfSir2 (deacetylase antagonizing acetylated H2B.Z) [#3]\"\n    ],\n    \"other_free_text\": [\n      \"H2B.Z occupancy correlates with promoter strength and AT-content but not stage-specific promoter timing [#1]\",\n      \"Acetylation state of H2B.Z governs its euchromatin-versus-heterochromatin partitioning and variant gene silencing [#3, #5]\",\n      \"Female-gametocyte-specific redistribution of H2B.Z into H3K9me3 heterochromatin [#4]\",\n      \"Variant expression declines in mid/late trophozoites, opposite to core histones [#7]\",\n      \"Distinct PTM pattern relative to canonical H2B [#2]\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_0714000","name":null,"product":"histone H2B variant","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_1420600","name":null,"product":"histone H2B variant, putative","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_1422900","name":null,"product":"histone H2B variant, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"","evaluation":null}