The Methyl-Histone H3 (Lys27) Antibody Sampler Kit provides an economical means of detecting levels of mono-, di-, and tri-methyl histone H3 Lys27 using methyl-specific and control histone H3 antibodies. The kit contains enough primary antibodies to perform at least two western blot experiments.

The nucleosome, made up of four core histone proteins (H2A, H2B, H3, and H4), is the primary building block of chromatin. Originally thought to function as a static scaffold for DNA packaging, histones have now been shown to be dynamic proteins, undergoing multiple types of post-translational modifications, including acetylation, phosphorylation, methylation, and ubiquitination (1). Histone methylation is a major determinant for the formation of active and inactive regions of the genome and is crucial for the proper programming of the genome during development (2,3). Arginine methylation of histones H3 (Arg2, 17, 26) and H4 (Arg3) promotes transcriptional activation and is mediated by a family of protein arginine methyltransferases (PRMTs), including the co-activators PRMT1 and CARM1 (PRMT4) (4). In contrast, a more diverse set of histone lysine methyltransferases has been identified, all but one of which contain a conserved catalytic SET domain originally identified in the Drosophila Su(var)3-9, Enhancer of zeste, and Trithorax proteins. Lysine methylation occurs primarily on histones H3 (Lys4, 9, 27, 36, 79) and H4 (Lys20) and has been implicated in both transcriptional activation and silencing (4). Methylation of these lysine residues coordinates the recruitment of chromatin modifying enzymes containing methyl-lysine binding modules such as chromodomains (HP1, PRC1), PHD fingers (BPTF, ING2), tudor domains (53BP1), and WD-40 domains (WDR5) (5-8). The discovery of histone demethylases, such as PADI4, LSD1, JMJD1, JMJD2, and JHDM1, has shown that methylation is a reversible epigenetic marker (9).

Methylation of histone H3 Lys27 is generally associated with transcriptional repression and regulation of stem cell pluripotency and differentiation, through the regulation of facultative heterochromatin. Mono-, di-, and tri-methylation of histone H3 Lys27 are all mediated by polycomb repressor complex 2 (PRC2), which contains either the EZH1 or EZH2 methyltransferase proteins. Tri- and di-methyl-histone H3 Lys27 levels are highest at the promoters of polycomb-repressed genes. In addition, tri- and di-methyl-histone H3 Lys27 is found at the promoters of inactive, but transcriptionally poised genes that also contain the active tri-methyl-histone H3 Lys4 modification. Mono-methyl-histone H3 Lys27 is more widely dispersed and found in the bodies of active genes.