Histone 3 (H3) is one of the four core histones (H2A, H2B, H3 and H4) fundamental in compacting eukaryotic DNA into the nucleosome. Similar to the other core histone, H3 has a globular domain and a flexible N-terminal domain, “histone tail” which can undergo modifications such as acetylation, methylation, phosphorylation and ubiquitination. Histone H3 is the most extensively modified of the five histones.
These histone modifications can alter the positioning of the nucleosome, allowing DNA to be either accessible or inaccessible to the transcription machinery. The modifications are carried out by histone modifying enzymes such as histone acetyltransferase (HATs) deacetylases (HDACs), histone methyltransferases (HMTs) and lysine demethylases (KDMs) and kinases and phosphatases. These histone modifications can occur in different complex combinations; making up what is known as the “histone code”. Alterations in the histone modification patterns, can result in cancers, autoimmune diseases and cardiovascular and neurodegenerative disorders.