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8228S 100 µl (50 tests) $299.00
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REACTIVITY SENSITIVITY Isotype
H M R Mk Endogenous Rabbit IgG
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Confocal immunofluorescent analysis of HeLa cells, untreated (left) or UV-treated (right), using Phospho-Histone H2A.X (Ser139) (20E3) Rabbit mAb (Alexa Fluor® 555 Conjugate) (red) and β-Tubulin (9F3) Rabbit mAb (Alexa Fluor® 488 Conjugate) #3623 (green).

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Immunofluorescence (Immunocytochemistry)

A. Solutions and Reagents

NOTE: Prepare solutions with reverse osmosis deionized (RODI) or equivalent grade water.

  1. 20X Phosphate Buffered Saline (PBS): (9808) To prepare 1L 1X PBS: add 50 ml 20X PBS to 950 ml dH2O, mix. Adjust pH to 8.0.
  2. Formaldehyde: 16%, methanol free, Polysciences, Inc. (cat# 18814), use fresh and store opened vials at 4°C in dark, dilute in 1X PBS for use.
  3. Blocking Buffer (1X PBS / 5% normal goat serum (#5425) / 0.3% Triton™ X-100): To prepare 10 ml: add 0.5 ml normal goat serum and 0.5 ml 20X PBS to 9.0 ml dH2O, mix. While stirring, add 30 µl Triton™ X-100.
  4. Antibody Dilution Buffer: (1X PBS / 1% BSA / 0.3% Triton™ X-100): To prepare 10 ml, add 30 µl Triton™ X-100 to 10 ml 1X PBS. Mix well then add 0.1 g BSA (#9998), mix.
  5. Prolong® Gold AntiFade Reagent (#9071), Prolong® Gold AntiFade Reagent with DAPI (#8961).

B. Specimen Preparation - Cultured Cell Lines (IF-IC)

NOTE: Cells should be grown, treated, fixed and stained directly in multi-well plates, chamber slides or on coverslips.

  1. Aspirate liquid, then cover cells to a depth of 2–3 mm with 4% formaldehyde diluted in 1X PBS.

    NOTE: Formaldehyde is toxic, use only in a fume hood.

  2. Allow cells to fix for 15 min at room temperature.
  3. Aspirate fixative, rinse three times in 1X PBS for 5 min each.
  4. Proceed with Immunostaining (Section C).

C. Immunostaining

NOTE: All subsequent incubations should be carried out at room temperature unless otherwise noted in a humid light-tight box or covered dish/plate to prevent drying and fluorochrome fading.

  1. Block specimen in Blocking Buffer for 60 min.
  2. While blocking, prepare primary antibody by diluting as indicated on datasheet in Antibody Dilution Buffer.
  3. Aspirate blocking solution, apply diluted primary antibody.
  4. Incubate overnight at 4°C.
  5. Rinse three times in 1X PBS for 5 min each.
  6. Coverslip slides with Prolong® Gold Antifade Reagent (#9071) or Prolong® Gold Antifade Reagent with DAPI (#8961).
  7. For best results, allow mountant to cure overnight at room temperature. For long-term storage, store slides flat at 4°C protected from light.

posted November 2006

revised November 2013

protocol id: 182

Product Usage Information

Application Dilutions
Immunofluorescence 1:50

Storage: Supplied in PBS (pH 7.2), less than 0.1% sodium azide and 2 mg/ml BSA. Store at 4°C. Do not aliquot the antibody. Protect from light. Do not freeze.

Specificity / Sensitivity

Phospho-Histone H2A.X (Ser139) (20E3) Rabbit mAb (Alexa Fluor® 555 Conjugate) detects endogenous levels of H2A.X only when phosphorylated at Ser139.


Species Reactivity: Human, Mouse, Rat, Monkey

Source / Purification

Monoclonal antibody is produced by immunizing animals with a synthetic phosphopeptide corresponding to residues surrounding Ser139 of human H2A.X.

Product Description

This Cell Signaling Technology antibody is conjugated to Alexa Fluor® 555 fluorescent dye and tested in-house for immunofluorescent analysis in human cells. The antibody is expected to exhibit the same species cross-reactivity as the unconjugated Phospho-Histone H2A.X (Ser139) (20E3) Rabbit mAb #9718.


Histone H2A.X is a variant histone that represents approximately 10% of the total H2A histone proteins in normal human fibroblasts (1). H2A.X is required for checkpoint-mediated cell cycle arrest and DNA repair following double-stranded DNA breaks (1). DNA damage, caused by ionizing radiation, UV-light, or radiomimetic agents, results in rapid phosphorylation of H2A.X at Ser139 by PI3K-like kinases, including ATM, ATR, and DNA-PK (2,3). Within minutes following DNA damage, H2A.X is phosphorylated at Ser139 at sites of DNA damage (4). This very early event in the DNA-damage response is required for recruitment of a multitude of DNA-damage response proteins, including MDC1, NBS1, RAD50, MRE11, 53BP1, and BRCA1 (1). In addition to its role in DNA-damage repair, H2A.X is required for DNA fragmentation during apoptosis and is phosphorylated by various kinases in response to apoptotic signals. H2A.X is phosphorylated at Ser139 by DNA-PK in response to cell death receptor activation, c-Jun N-terminal Kinase (JNK1) in response to UV-A irradiation, and p38 MAPK in response to serum starvation (5-8). H2A.X is constitutively phosphorylated on Tyr142 in undamaged cells by WSTF (Williams-Beuren syndrome transcription factor) (9,10). Upon DNA damage, and concurrent with phosphorylation of Ser139, Tyr142 is dephosphorylated at sites of DNA damage by recruited EYA1 and EYA3 phosphatases (9). While phosphorylation at Ser139 facilitates the recruitment of DNA repair proteins and apoptotic proteins to sites of DNA damage, phosphorylation at Tyr142 appears to determine which set of proteins are recruited. Phosphorylation of H2A.X at Tyr142 inhibits the recruitment of DNA repair proteins and promotes binding of pro-apoptotic factors such as JNK1 (9). Mouse embryonic fibroblasts expressing only mutant H2A.X Y142F, which favors recruitment of DNA repair proteins over apoptotic proteins, show a reduced apoptotic response to ionizing radiation (9). Thus, it appears that the balance of H2A.X Tyr142 phosphorylation and dephosphorylation provides a switch mechanism to determine cell fate after DNA damage.


1.  Yuan, J. et al. (2010) FEBS Lett 584, 3717-24.

2.  Mukherjee, B. et al. (2006) DNA Repair (Amst) 5, 575-90.

3.  Solier, S. et al. (2009) Mol Cell Biol 29, 68-82.

4.  Lu, C. et al. (2006) Mol Cell 23, 121-32.

5.  Lu, C. et al. (2008) FEBS Lett 582, 2703-8.

6.  Cook, P.J. et al. (2009) Nature 458, 591-6.

7.  Rogakou, E.P. et al. (1998) J. Biol. Chem. 273, 5858-5868.

8.  Xiao, A. et al. (2009) Nature 457, 57-62.

9.  Burma, S. et al. (2001) J. Biol. Chem. 276, 42462-42467.

10.  Rogakou, E.P. et al. (1999) J. Cell Biol. 146, 905-916.


Entrez-Gene Id 3014
Swiss-Prot Acc. P16104


For Research Use Only. Not For Use In Diagnostic Procedures.
Cell Signaling Technology® is a trademark of Cell Signaling Technology, Inc.
The Alexa Fluor® dye antibody conjugates in this product are sold under license from Life Technologies Corporation for research use only, except for use in combination with DNA microarrays. The Alexa Fluor® dyes (except for Alexa Fluor® 430 dye) are covered by pending and issued patents. Alexa Fluor® is a registered trademark of Molecular Probes, Inc.
U.S. Patent No. 5,675,063.