Antibodies to Modified Histones

In eukaryotic cells DNA is associated with histones and other proteins to form chromatin. The basic unit of chromatin is the nucleosome consisting of 140 bp of DNA wrapped around an octameric core of the four conserved histones H2A, H2B, H3 and H4.

The relatively unstructured and highly charged N-terminal tail domains of histones, are central to the processes that modulate chromatin structure. A diverse and elaborate array of post-translational modifications that include acetylation, phosphorylation, methylation, ubiquitination and ADP-ribosylation, occur on the N-terminal tail domains of histones. Acetylation of lysine residues within these N-terminal domains by histone acetyl-transferases (HATs), is associated with transcriptional activation. This modification results in remodeling of the nucleosome structure into an open conformation more accessible to transcription complexes. In most species, histone H3 is primarily acetylated at lysines 9, 14, 18 and 23. Acetylation at lysine 9 appears to have a dominant role in histone deposition and chromatin assembly in some organisms. Phosphorylation of H3, referred to as the nucleosomal response, is localized to a small fraction of highly acetylated H3 and occurs primarily in response to mitogenic and stress stimuli. Phosphorylation of histone H3 on Ser¹⁰ is highly correlated with chromosome condensation during both mitosis and meiosis. Phosphorylation at this site is also directly correlated with the induction of immediate-early genes such as c-jun, c-fos and c-myc. PKA, Rsk-2 and Msk-1 are necessary for the histone H3 phosphorylation. Activation of both ERK and p38 MAP Kinase pathways by mitogenic stimuli, have been suggested to modulate the phosphorylation of histone H3.