H2A

PF3D7_0617800 encodes the canonical core histone H2A of Plasmodium falciparum, a nucleosome-packaging protein whose expression is developmentally coupled to DNA replication, peaking in late trophozoite stages while being absent in rings (PMID:16410041, PMID:10579431). Reconstituted nucleosomes containing parasite H2A display reduced salt and thermal stability and lower affinity for GC-rich DNA relative to their human counterparts, defining a biochemically distinct chromatin platform in P. falciparum (PMID:28033404). H2A deposition is handled by dedicated histone chaperones: it binds PfNapS as part of the core histone assembly, and PfNPM engages assembled H2A/H2B dimers via its acidic tracts, with H3/H4 outcompeting H2A/H2B for the same chaperone surface (PMID:20377878, PMID:40049416). Beyond its structural role, H2A functionally substitutes for the missing H2A.X variant in the DNA damage response: it is phosphorylated on serine 121 upon double-strand breaks, and this γ-PfH2A mark is recruited to damage foci and dynamically removed as repair proceeds, recruiting the acetyltransferase PfMYST to those sites (PMID:33441412, PMID:38564734). H2A is additionally a substrate for arginine methylation by PfPRMT1 in vitro and carries a broader set of mapped post-translational modifications (PMID:19344311, PMID:19351122).

1. 1992 Low

   Establishing the molecular identity of the parasite's canonical H2A gene was the necessary first step to studying its chromatin biology.

   Evidence Molecular cloning and sequence-level gene identification in P. falciparum

   PMID:1518525

   Open questions at the time

   • No functional or mechanistic characterization at this stage
   • Protein expression and localization not yet addressed
2. 1997 Medium

   Confirming that the encoded protein is a bona fide core histone localized to the nucleus grounded H2A as a genuine chromatin component rather than a predicted ORF.

   Evidence Acid extraction/purification, N-terminal sequencing, and immunofluorescence localization to schizont nuclei

   PMID:9149412

   Open questions at the time

   • Stage-resolved expression not quantified
   • No interaction partners identified
3. 1999 Low

   Defining stage-specific transcription linked H2A expression to the parasite's replicative program rather than constant chromatin turnover.

   Evidence Transcript profiling across developmental stages showing absence in rings and elevated levels in trophozoites, schizonts, and gametocytes

   PMID:10579431

   Open questions at the time

   • Transcript-level only, protein dynamics not measured
   • Mechanism coupling expression to replication unknown
4. 2006 Medium

   Confirming protein-level synthesis and a late-trophozoite expression surge tied H2A abundance directly to replication-phase nucleosome assembly.

   Evidence Mass spectrometry, real-time RT-PCR, and immunoblotting across erythrocytic stages

   PMID:16410041

   Open questions at the time

   • Causal role of the expression surge in replication not tested
   • Assembly machinery not identified here
5. 2009 Medium

   Identifying H2A as a PfPRMT1 substrate and cataloging its post-translational modifications opened the question of how H2A marks regulate parasite chromatin.

   Evidence In vitro methyltransferase assay with recombinant PfPRMT1; global LC-MS/MS histone PTM mapping

   PMID:19344311 PMID:19351122

   Open questions at the time

   • Arginine methylation site on H2A not mapped
   • In vivo relevance of the methylation not established
   • Functional readout of mapped PTMs unknown
6. 2010 Medium

   Mapping chaperone and nuclear-protein interactions began to define how H2A is handled during assembly and how it engages the nuclear proteome.

   Evidence Fluorescence spectroscopy binding with PfNapS plus PfNapS crystal structure; bacterial two-hybrid screen against PfTudor-SN

   PMID:20377878 PMID:20713134

   Open questions at the time

   • PfTudor-SN interaction lacks orthogonal validation
   • Functional consequence of the PfNapS interaction not tested in vivo
7. 2016 High

   Demonstrating that parasite H2A forms less stable nucleosomes than human H2A revealed an intrinsic biochemical distinctness of Plasmodium chromatin.

   Evidence In vitro nucleosome reconstitution with salt stability, thermal mobility, and GC-rich DNA binding assays comparing human and parasite histones

   PMID:28033404

   Open questions at the time

   • Structural basis of reduced stability not resolved
   • In vivo consequence for genome accessibility not tested
8. 2021 High

   Showing that canonical H2A is phosphorylated on Ser121 and recruited to damage foci established that H2A functionally replaces the absent H2A.X variant in the parasite's DNA damage response.

   Evidence Phospho-specific immunofluorescence, live imaging, and DNA damage assays with genotoxic agents

   PMID:33441412

   Open questions at the time

   • Kinase responsible for S121 phosphorylation not identified
   • Phosphatase removing the mark not defined
   • Downstream repair effectors reading γ-PfH2A not mapped
9. 2024 Medium

   Linking PfMYST recruitment to γ-PfH2A foci placed H2A phosphorylation upstream of a specific chromatin-modifying effector in the damage response.

   Evidence Western blotting, immunofluorescence co-localization, and PfMYST overexpression/knockdown

   PMID:38564734

   Open questions at the time

   • Direct physical interaction between PfMYST and γ-PfH2A not shown
   • Repair outcome dependence on PfMYST recruitment not quantified
10. 2025 High

    Defining the stoichiometry and acidic-tract dependence of PfNPM binding to H2A/H2B refined how the parasite chaperone system stores and hands off core histones.

    Evidence Crystal structure, binding affinity measurements, acidic-tract mutagenesis, and size-exclusion chromatography

    PMID:40049416

    Open questions at the time

    • In vivo role of PfNPM in H2A deposition not established
    • Competition with H3/H4 not tested in cells

• The kinase/phosphatase circuit controlling S121 phosphorylation, the in vivo function of H2A arginine methylation, and the physiological consequences of the intrinsically unstable parasite nucleosome remain unresolved.
• Enzymes writing and erasing γ-PfH2A not identified
• Functional impact of reduced nucleosome stability on genome regulation untested
• No loss-of-function genetics for PF3D7_0617800 itself in the corpus