Histones and Histone Modifications

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Related Resources: Brochures | Application Notes
Histones play a critical role in packaging DNA in the eukaryotic nucleus and are heavily regulated by post-translational histone modifications. The core histones (H2A, H2B, H3, H4) assemble as dimers into structures called nucleosomes that have approximately 146 bp of DNA spooled them locked in place by linker histone H1. Although histone content of each nucleosome is largely the same, histone proteins are subject to a variety of post-translational modifications (e.g. phosphorylation, methylation, acetylation, ubiquitination, and citrullination). These histone modifications occur at specific locations and create what is often called the histone code. These modified histones allow the generation of a diverse collection of nucleosomes which can be recognized by other chromatin associated proteins. This coordinated interaction of histones, modified histones and non-histone proteins can alter local chromatin structure and influence a variety of cellular functions such as transcription, repair, recombination, and replication.

Merck grasps the complexity of the histone code and the need for highly specific antibodies. To enable the study of histone and epigenetic regulation, we offer over 600 histone antibodies, antibody conjugates and recombinant proteins.

Advantages of Merck Histone Antibodies

  • Large offering of antibodies against important modified histones, histone variants and histone mutants
  • Validated for a variety of applications including ChIP, ChIP-seq. Western Blotting, Immunocytochemistry 
  • Specificity verified by approaches such as AbSurance Histone Peptide Arrays
  • Consistent performance lot-to-lot
  • Extensively published in peer-reviewed publications
  • Back by in-house expertise in the development of epigenetics kits and assays
  • Trial size antibodies available
  • Histone antibody conjugates available

To browse our collection of antibodies and proteins against modified and unmodified histone, click on the check marks in the table below.

H1
H2A
H2B
H3
H4
Unmodified Histones
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Acetylated
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Phosphorylated
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Methylated
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Ubiquitinated Merck:/Freestyle/BI-Bioscience/Antibodies-Assays/epigenetics-images/epi_check.gif Merck:/Freestyle/BI-Bioscience/Antibodies-Assays/epigenetics-images/epi_check.gif
Citrullinated
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Proteins and Peptides
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ChIP Ab+ and Kits
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Histones

Although histones are often modified, unmodified histones are also useful for epigenetics research as controls or for establishing basal levels. Merck offers validated antibodies to histone H1, H2A, H2B, H3, H4, H2A.Z, H2A.X and other histone variants as well as mutated histones such as the glioblastoma associated mutation of Histone H3 lysine 27 to methionine (H3K27M).

Acetylation

Histone acetylases (HATs) and deacetylases (HDACs) are key regulators of gene expression and function. Transcription activation complexes contain HATs, which add an acetyl group to conserved histone lysines on histone proteins. In most cases acetylation will open chromatin structure to permit transcription. Conversely, HDACs remove acetyl groups, typically leading to decreased gene expression.

Methylation

Histones can be mono, di or trimethylated at lysine and arginine residues. Methylation of certain histone residues is indicative of euchromatin (loosely packed chromatin) and transcriptional activation, while other methylation events are hallmarks of heterochromatin (densely packed chromatin) and correlate with transcriptional repression. Both the location of these methylation marks and the degree of methylation at a site (mono, di, or tri) influences the degree of packing as well as the recruitment of other histone associated proteins to a specific site.

Histone methylation can be reversed by site specific histone demethylases, such as LSD1, UTX, and the JMJD family of enzymes. The coordinated activity of histone methylases and demethylases temporally and spatially regulates gene expression, particularly during embryonic development.

Phosphorylation

Phosphorylation of histones commonly occurs during chromosome condensation in mitosis, in cells undergoing apoptosis, and in response to DNA damage. However, certain histone sites are phosphorylated in response to very early gene induction signaling. In these instances, histone phosphorylation may promote either opening or closing of chromatin structure, depending on site and cellular context.

Ubiquitination

Ubiquitination is required for certain histone methylation events and involves ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s), and ubiquitin protein ligases (E3s). Our wide range of products for measuring ubiquitination includes unique antibodies for specific ubiquitin linkages and modified histone residues such as Histone H2A ubiquitinated at Lys119.

Citrullination

Citrullination is a modification of arginine that may play a role in rheumatoid arthritis and multiple sclerosis. Approximately 10% of histones are citrullinated, suggesting a role for citrulline in gene regulation. EMD Millipore offers a site-specific antibody to citrullinated histone H4, as well as antibodies and assays to detect this unique modification.
Featured Antibody:
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Click image to enlarge.
A431 cells were stained using Anti-trimethyl-Histone H3 (Lys4), Alexa Fluor® 647 (Cat. No. 07-473-AF647, pink). Actin filaments have been labeled with Phalloidin-Alexa Fluor® 488 (green). Nuclei are stained with DAPI (Blue). This antibody positively stains the nucleus.

AbSurance™ Histone Antibody Specificity Arrays

To prevent ambiguous or misleading results histone antibodies must be highly specific and not cross react other modified or non-modified sites. At EMD Millipore we carefully screen our histone antibodies for cross reactivity. While this can be done by a variety of methods, we most frequently use histone peptide dot blots. To enable researchers to easily perform this screening in their labs, we offer a version of the dot blots we use in our own lab. The AbSurance™ Histone Antibody Specificity Arrays are macroarrays that follow a Western blot workflow and can be read by eye eliminating the need for any specialized array scanners or software.  
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These essential screening tools allow researchers to demonstrate and verify the specificity and cross-reactivity of antibodies in advance of critical experiments. Antibodies for histones H2A, H2B, H3, H4, and their post-translational modifications can be evaluated using these arrays. To cover the range of histone modification sites, two arrays provide a total of 89 unique high quality peptides in 10 ng and 100 ng quantities to easily detect both strong and weak cross-reactivity. The H3 Array provides 8 acetylated, 27 methylated, 5 phosphorylated, and 6 unmodified peptides of histone H3. The H2A, H2B, H4 Array offers 13 acetylated, 16 methylated, 6 phosphorylated, and 8 unmodified peptides of H2 and H4. Additional rat, sheep, rabbit, and mouse primary antibodies are spotted on each array for convenient built-in positive controls. To screen the combinatorial histone code, or for the evaluation of the interactions of histone reader, writer, and erasers, and microarray version of this product, the AbSurance™ Pro Histone Peptide Microarray is also available.

Featured Product

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Specificity Ccreening of Histone H3 Antibodies
I.
The Histone H3 Array was probed with Anti-trimethyl histone H3 (Lys4) (Cat.No. 05-745R, 1µg/mL). Peptides and control IgG were visualized using a donkey Anti-rabbit IgG, peroxidase conjugated, H+L (Cat. No. AP182P) and a chemiluminescent detection system.
II.
The Histone H3 Array was probed with Anti-dimethyl histone H3 (Lys4) (Cat. No. 05-1338, 1µg/mL). Peptides were visualized using a goat anti-mouse IgG peroxidase conjugated, H+L (Cat. No. AP124P) and a chemiluminescence detection system.
III.
Peptide map showing reactive peptide spots on Figure 1(I) (RED) and Figure 1(II) (BLUE). Respective species-specific control IgG, which reacted with the secondary antibody used, is shown in a lighter shade of each color.