Common Histone H3

Histone H3 is one of the five main histones involved in the structure of chromatin in eukaryotic cells. Featuring a main globular domain and a long N-terminal tail, H3 is involved with the structure of the nucleosomes of the 'beads on a string' structure. Histone proteins are highly post-translationally modified however Histone H3 is the most extensively modified of the five histones. Histone H3 is an important protein in the emerging field of epigenetics, where its sequence variants and variable modification states are thought to play a role in the dynamic and long-term regulation of genes.

Histone modification often includes methylation, phosphorylation, acetylation, ubiquitylation, Lysines can be either mono-, di-, or tri-methylated, forming functional diversity to each site of methylation. For instance, both mono- or tri-methylation of K4 (H3K4me1 or H3K4me3) are active marks, but H3K4me1 is found at transcriptional enhancers, while H3K4me3 is found at gene promoters. Tri-methylation of K36 (H3K36me3) is associated with transcribed regions in gene bodies. Tri-methylation of K9 and K27 on histone H3 (H3K27me3 and H3K9me3) are both repressive signals, however, H3K27me3 is a temporary signal that controls development regulators. Conversely, H3K9me3 is a permanent signal for heterochromatin formation of chromosomal regions with tandem repeat structures.