GO:0035979 histone H2AXS139 kinase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0035979 describes the catalytic activity that transfers a phosphate from ATP onto serine 139 of histone variant H2AX, producing gamma-H2AX.
• This activity is the molecular definition of the DNA damage response kinase step performed by PIKK-family enzymes such as ATM, ATR and DNA-PKcs.
• H2AX phosphorylation at S139 is a conserved epigenetic mark that influences chromatin organization and stem cell radioresponses.
• The mark is mechanistically linked to DNA repair processes and to checkpoint signaling through Chk1 phosphorylation in human cells.
• Loss or dysregulation of H2AX S139 phosphorylation alters proliferation, chromatin compaction and repair efficiency.
• CRISPR knockout, point-mutation and knock-in models are the standard tools for dissecting the causal role of this activity in cells.
Description
GO:0035979, histone H2AXS139 kinase activity, is a molecular function term in the Gene Ontology that captures the enzymatic addition of a phosphate group to serine 139 of the histone variant H2AX. The reaction consumes ATP and converts H2AX-serine 139 into H2AX-phosphoserine 139, generating the chromatin mark widely known as gamma-H2AX. Because this modification is one of the earliest and most abundant signals generated at sites of DNA damage, the activity defined by GO:0035979 sits at the interface of chromatin biology, genome maintenance and cell cycle checkpoint control. Researchers studying genome stability, radioresponses and epigenetic regulation therefore treat this activity as a central node for experimental interrogation. The term is also relevant to stem cell biology, where H2AX phosphorylation and accompanying histone modifications shape how normal stem cells respond to radiation. Understanding which kinases perform this reaction, how the reaction is regulated, and what downstream processes it controls is essential for interpreting DNA damage response phenotypes in health and disease.
histone H2AXS139 kinase activity At A Glance
| GO ID | GO:0035979 |
|---|---|
| GO term | histone H2AXS139 kinase activity |
| Ontology | molecular_function |
| Synonym | histone H2AS139 kinase activity; histone kinase activity (H2A-S139 specific); histone kinase activity (H2A.x-S139 specific) |
| Major function | Catalyzes ATP-dependent phosphorylation of histone H2AX at serine 139, producing gamma-H2AX |
| Reaction | histone H2AX-serine (position 139) + ATP = histone H2AX-phosphoserine (position 139) + ADP |
| Substrate | Histone variant H2AX, specifically serine 139 |
| Cofactor | ATP as phosphate donor |
| Biological context | DNA damage response, chromatin remodeling and checkpoint signaling |
What Is GO:0035979?
In plain terms, GO:0035979 is the activity of an enzyme that puts a phosphate tag on a specific histone protein. More precisely, it catalyzes the reaction in which histone H2AX serine at position 139 plus ATP yields histone H2AX phosphoserine at position 139 plus ADP. The activity is specific for the serine 139 position of the histone variant H2AX, which is why the synonyms include histone H2AS139 kinase activity and histone kinase activity (H2A.x-S139 specific). The product of this reaction, phosphorylated H2AX at S139, is the molecular event that converts a DNA damage signal into a chromatin-bound mark recognized by downstream repair and checkpoint machinery.
Why Is histone H2AXS139 kinase activity Important in Cell Biology?
GO:0035979 matters because it defines the enzymatic step that installs one of the most widely used biomarkers of DNA damage, gamma-H2AX, and because the activity is mechanistically coupled to repair, chromatin reorganization and checkpoint control. Experimental work shows that perturbing this axis, for example by silencing chromatin modifiers, alters HP1-positive chromatin, stimulates DNA repair processes and dysregulates proliferation through Chk1 phosphorylation in human endothelial cells. In normal stem cells, H2AX phosphorylation together with H3K56 acetylation exerts a unique epigenetic influence on radioresponses, indicating that the activity defined by GO:0035979 shapes how stem cells survive or fail after genotoxic stress. Consequently, the term is a practical anchor for researchers designing CRISPR models, interpreting gamma-H2AX imaging, or screening for modulators of genome stability.
• Provides the molecular definition of the kinase step that generates gamma-H2AX, a canonical DNA damage marker.
• Links chromatin modification directly to DNA repair pathway activation.
• Influences cell cycle checkpoint signaling through Chk1 phosphorylation.
• Shapes proliferation dynamics in human endothelial cells when chromatin regulators are perturbed.
• Contributes to the epigenetic control of normal stem cell radioresponses.
• Connects histone variant biology with H3K56 acetylation in stem cell chromatin.
• Serves as a functional readout for genotoxic exposure in experimental models.
• Is a tractable target for CRISPR knockout and point-mutation studies of DNA damage signaling.
Molecular Mechanism of histone H2AXS139 kinase activity
Substrate recognition and ATP-dependent phosphate transfer
In simple terms: The enzyme finds a specific spot on a histone protein and attaches a phosphate tag using ATP as the phosphate source.
The activity defined by GO:0035979 catalyzes the reaction histone H2AX-serine (position 139) + ATP = histone H2AX-phosphoserine (position 139) + ADP. Substrate specificity is directed to serine 139 of the histone variant H2AX, distinguishing this activity from other histone kinases. The reaction consumes ATP and produces ADP plus the phosphorylated histone product, which is the molecular event that generates gamma-H2AX.
Coupling to DNA damage response signaling
In simple terms: When DNA is damaged, this kinase activity marks the surrounding chromatin so repair and checkpoint proteins can assemble there.
H2AX phosphorylation at S139 is mechanistically coupled to DNA repair processes and to checkpoint signaling, as demonstrated in human endothelial cells where perturbation of chromatin regulators stimulated DNA repair and dysregulated proliferation via Chk1 phosphorylation. This places GO:0035979 upstream of repair factor recruitment and checkpoint activation.
Chromatin context and epigenetic interplay
In simple terms: The phosphate tag does not act alone; it works together with other histone modifications to change how chromatin behaves.
H2AX phosphorylation exerts a unique epigenetic influence together with H3K56 acetylation on normal stem cell radioresponses, indicating that the activity defined by GO:0035979 operates within a combinatorial histone modification landscape. In endothelial cells, silencing the histone demethylase LSD1 increased HP1-positive chromatin alongside stimulated DNA repair, showing that chromatin state modulates the consequences of H2AX S139 phosphorylation.
Downstream effects on proliferation and genome stability
In simple terms: The mark ultimately affects whether cells divide normally or stall, especially after damage.
Dysregulation of proliferation through Chk1 phosphorylation follows perturbation of the chromatin and repair axis associated with H2AX phosphorylation in human endothelial cells. In stem cells, the combined influence of H2AX phosphorylation and H3K56 acetylation shapes radioresponses, linking GO:0035979 to survival decisions after genotoxic stress.
Key Genes Involved in GO:0035979 histone H2AXS139 kinase activity
The genes and proteins below are the experimentally documented components and modifiers connected to histone H2AXS139 kinase activity and its downstream chromatin and checkpoint effects.
| Gene | Major Role | Research Relevance |
|---|---|---|
| H2AX | Histone variant substrate phosphorylated at S139 | Core substrate defining GO:0035979; gamma-H2AX readout |
| ATM | PIKK-family kinase that phosphorylates H2AX at S139 in response to damage | Central effector of the DNA damage response |
| ATR | PIKK-family kinase acting in replication stress responses | Related S139 kinase in checkpoint signaling |
| DNA-PKcs | PIKK-family kinase involved in non-homologous end joining | Candidate S139 kinase in repair contexts |
| LSD1 (KDM1A) | Lysine-specific histone demethylase | Silencing increases HP1-positive chromatin and stimulates DNA repair |
| HP1 | Heterochromatin protein | Marker of chromatin compaction altered by LSD1 silencing |
| Chk1 (CHEK1) | Checkpoint kinase | Phosphorylation dysregulated with proliferation changes |
| H3K56 | Histone H3 residue subject to acetylation | Interplays with H2AX phosphorylation in stem cell radioresponses |
| H3K56 acetyltransferases | Enzymes depositing H3K56 acetylation | Modulate the epigenetic context of H2AX phosphorylation |
| H3K56 deacetylases | Enzymes removing H3K56 acetylation | Modulate the epigenetic context of H2AX phosphorylation |
| DNA repair factors | Proteins recruited to gamma-H2AX-marked chromatin | Downstream effectors of the S139 mark |
| Endothelial cell proliferation regulators | Proteins controlling cell cycle progression | Phenotype altered when the LSD1-H2AX-Chk1 axis is perturbed |
| Stem cell radioresponse regulators | Proteins governing survival after radiation | Influenced by H2AX phosphorylation and H3K56 acetylation |
| Chromatin remodeling complexes | Machines that reposition nucleosomes | Determine accessibility around phosphorylated H2AX |
| Checkpoint adaptor proteins | Scaffolds transmitting damage signals | Link gamma-H2AX to Chk1 activation |
| Histone variant deposition machinery | Factors that incorporate H2AX into nucleosomes | Determine substrate availability for GO:0035979 |
How Is histone H2AXS139 kinase activity Regulated?
The activity defined by GO:0035979 is regulated at the level of chromatin context and histone modification crosstalk. Silencing the histone demethylase LSD1 increases HP1-positive chromatin, stimulates DNA repair processes and dysregulates proliferation through Chk1 phosphorylation in human endothelial cells, showing that chromatin-modifying enzymes set the permissive state for H2AX S139 phosphorylation and its downstream signaling. In normal stem cells, H2AX phosphorylation acts together with H3K56 acetylation to exert a unique epigenetic influence on radioresponses, indicating that the acetylation status of neighboring histone residues modulates the functional outcome of the S139 mark.
histone H2AXS139 kinase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| H2AX | Genome instability and DNA damage response | H2AX S139 point-mutation knock-in cell line |
| LSD1 (KDM1A) | Endothelial proliferation and chromatin compaction | LSD1 knockout endothelial cell model |
| Chk1 (CHEK1) | Checkpoint dysregulation and proliferation | Chk1 phosphorylation reporter knock-in |
| H3K56 acetylation machinery | Stem cell radioresponse | Stem cell knockout of H3K56 acetyltransferase/deacetylase |
| ATM/ATR/DNA-PKcs | DNA damage signaling and repair | Kinase-dead point-mutation knock-in models |
Cancer and genome instability
Because GO:0035979 generates gamma-H2AX, a canonical marker of DNA damage, its dysregulation is mechanistically tied to genome instability, a hallmark of cancer. Perturbation of the chromatin and repair axis involving H2AX phosphorylation alters proliferation through Chk1 phosphorylation in human endothelial cells, illustrating how this activity influences cell cycle control relevant to tumor biology.
Radiation response and tissue injury
H2AX phosphorylation and H3K56 acetylation uniquely influence normal stem cell radioresponses, linking the activity defined by GO:0035979 to how tissues respond to radiation-induced damage. This has implications for understanding radiosensitivity and for interpreting gamma-H2AX as a biomarker after genotoxic exposure.
Vascular and endothelial biology
In human endothelial cells, silencing LSD1 causes increased HP1-positive chromatin, stimulation of DNA repair processes and dysregulation of proliferation by Chk1 phosphorylation, directly connecting the chromatin context of H2AX S139 phosphorylation to endothelial cell behavior.
From histone H2AXS139 kinase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Is H2AX S139 phosphorylation required for repair factor recruitment? | H2AX S139A point-mutation knock-in |
| Which kinase performs GO:0035979 in a given cell type? | ATM, ATR or DNA-PKcs knockout cells |
| How does chromatin compaction affect the S139 mark? | LSD1 knockout endothelial cells |
| Does H3K56 acetylation modify stem cell radioresponses? | H3K56 acetylation machinery knockout stem cells |
| Can gamma-H2AX be tracked dynamically? | Tagged H2AX knock-in with fluorescent reporter |
| Does overexpression of a candidate kinase increase S139 phosphorylation? | Overexpression cell model with gamma-H2AX readout |
How to Study the histone H2AXS139 kinase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Gamma-H2AX immunofluorescence | Nuclear foci of phosphorylated H2AX S139 | DNA damage and repair quantification |
| Immunoblotting for gamma-H2AX | Total levels of H2AX S139 phosphorylation | Kinase activity readout |
| Chk1 phosphorylation immunoblot | Checkpoint kinase activation | Proliferation and checkpoint studies |
| HP1 chromatin staining | Heterochromatin compaction | Chromatin state assessment |
| H3K56 acetylation profiling | Histone acetylation status | Stem cell radioresponse studies |
| Proliferation assays | Cell cycle progression | Phenotypic consequence of S139 mark |
| CRISPR knockout screening | Gene requirement for S139 phosphorylation | Candidate kinase discovery |
| Point-mutation knock-in | Requirement of specific residues | Causal testing of H2AX S139 |
Gamma-H2AX detection by immunofluorescence and immunoblotting
Because GO:0035979 produces phosphorylated H2AX at S139, the standard readout is detection of gamma-H2AX foci or signal by antibody-based methods. These assays are used to quantify DNA damage and repair kinetics in cell models where the activity is perturbed.
Chromatin and histone modification profiling
Evaluating HP1-positive chromatin and H3K56 acetylation alongside H2AX phosphorylation provides a combinatorial view of how the S139 mark operates within chromatin. Such profiling is essential when interpreting stem cell radioresponses or endothelial chromatin changes.
Checkpoint and proliferation assays
Measuring Chk1 phosphorylation and proliferation parameters allows researchers to connect the activity defined by GO:0035979 to downstream cell cycle outcomes. These assays are typically paired with chromatin perturbation experiments.
CRISPR-based genetic perturbation
Knockout, point-mutation and knock-in strategies are used to test causality of candidate kinases and histone residues in generating the S139 mark and its downstream effects.
How CRISPR Can Be Used to Study GO:0035979 histone H2AXS139 kinase activity
Knockout
CRISPR knockout of candidate kinases such as ATM, ATR or DNA-PKcs, or of chromatin modifiers like LSD1, allows researchers to test which factors are required for histone H2AXS139 kinase activity and its downstream effects on proliferation and Chk1 phosphorylation.
Point Mutation
Introducing a point mutation that converts H2AX serine 139 to a non-phosphorylatable residue provides a direct causal test of whether the activity defined by GO:0035979 is required for repair factor recruitment and checkpoint signaling.
Knock-in
Knock-in of tagged or reporter-linked H2AX enables dynamic tracking of the S139 phosphorylation mark in live cells and in stem cell radioresponse experiments where H2AX phosphorylation and H3K56 acetylation act together.
Overexpression
Overexpression of a candidate kinase or of H2AX itself can be used to determine whether increased substrate or enzyme availability elevates gamma-H2AX levels and alters proliferation or chromatin state.
How EDITGENE Supports histone H2AXS139 kinase activity Research
Researchers studying histone H2AXS139 kinase activity-related genes often need to determine whether a candidate gene is causally involved in generating the S139 mark, in chromatin reorganization, or in downstream checkpoint and proliferation phenotypes. Establishing causality requires precise genetic models in which a single gene, residue or regulatory element is altered without confounding background changes. EDITGENE provides the full spectrum of CRISPR cell model engineering and screening services needed to interrogate GO:0035979 from substrate to phenotype.
Contact EDITGENE today to design your custom CRISPR model for histone H2AXS139 kinase activity research.
Frequently Asked Questions About histone H2AXS139 kinase activity
What is histone H2AXS139 kinase activity?
It is the enzymatic activity defined by GO:0035979 that transfers a phosphate from ATP to serine 139 of histone H2AX, producing gamma-H2AX.
What does GO:0035979 mean?
GO:0035979 is the Gene Ontology molecular function term for the catalysis of histone H2AX serine 139 phosphorylation.
What genes are involved in histone H2AXS139 kinase activity?
Key genes include H2AX as the substrate and PIKK-family kinases such as ATM, ATR and DNA-PKcs, along with chromatin modifiers like LSD1 and checkpoint effectors such as Chk1.
What is the reaction catalyzed by GO:0035979?
The reaction is histone H2AX-serine (position 139) + ATP = histone H2AX-phosphoserine (position 139) + ADP.
Why is gamma-H2AX important in DNA damage research?
Gamma-H2AX is the product of the activity defined by GO:0035979 and serves as a widely used marker of DNA damage and repair.
How is H2AX S139 phosphorylation linked to Chk1?
Perturbation of the chromatin and repair axis involving H2AX phosphorylation dysregulates proliferation through Chk1 phosphorylation in human endothelial cells.
Does H2AX phosphorylation affect stem cell radiation responses?
Yes, H2AX phosphorylation together with H3K56 acetylation exerts a unique epigenetic influence on normal stem cell radioresponses.
How can I study histone H2AXS139 kinase activity with CRISPR?
Knockout of candidate kinases, point mutation of H2AX S139, tagged knock-in of H2AX and overexpression models are all suitable CRISPR strategies.
What synonyms are used for GO:0035979?
Synonyms include histone H2AS139 kinase activity and histone kinase activity (H2A.x-S139 specific).
Which assays measure histone H2AXS139 kinase activity?
Gamma-H2AX immunofluorescence and immunoblotting, Chk1 phosphorylation assays, HP1 chromatin staining and H3K56 acetylation profiling are commonly used.
Conclusion
GO:0035979, histone H2AXS139 kinase activity, defines the ATP-dependent reaction that installs the gamma-H2AX mark on serine 139 of histone H2AX. This activity is mechanistically coupled to DNA repair, chromatin reorganization and checkpoint signaling, and it shapes proliferation and stem cell radioresponses. Because the mark is both a functional event and a widely used biomarker, precise genetic models are essential for causal studies. CRISPR knockout, point-mutation, knock-in and overexpression approaches provide the experimental resolution needed to dissect how this activity contributes to genome stability and disease.
References
- 1. Wojtala M et al.. 2019. Silencing Lysine-Specific Histone Demethylase 1 (LSD1) Causes Increased HP1-Positive Chromatin, Stimulation of DNA Repair Processes, and Dysregulation of Proliferation by Chk1 Phosphorylation in Human Endothelial Cells.. Cells 8(10) PMID: 31591366
- 2. Jacobs KM et al.. 2016. Unique epigenetic influence of H2AX phosphorylation and H3K56 acetylation on normal stem cell radioresponses.. Mol Biol Cell 27(8):1332-45 PMID: 26941327
