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Background
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Histones are a family of basic proteins, which associate with nuclear DNA. Histones are essential for the folding and condensing of nuclear DNA to form nucleosomes and chromatin in eukaryotes. The compressed form of chromatin inhibits the interaction of transcription enzymes with DNA. A nucleosome consists of approximately 146 base pairs of DNA wrapped around a histone octamer to make the basic unit of chromatin structure. The Octamer is comprised of histones (H2A, H2B, H3 and H4) and about 200 bases of nucleic acid to form a nucleosome. Histones consist of a globular domain and a more flexible amino acid terminal domain. The histone tail that protrudes out from the nucleosomal surface can be modified by methylation, phosphorylation, ubiquitination and ADP ribosylation and biotinylation. These post translational modifications affect the structure of chromatin and are involved in DNA repair, mitotic and meiotic chromosome condensation and gene regulation. Histone H3 is a 17 kDa nuclear protein that is a component of an octamer containing pairs of each of four core histones (H2A, H2B, H3, and H4). Histone H3 is one of the five main histone proteins involved in the structure of chromatin in eukaryotic cells and has several sequence variants and post translational modification states that regulate the epigenetic control of genes. Histone H3 is involved with the structure of the nucleosomes of the 'beads on a string' structure. The N-terminal tail of histone H3 undergoes several different types of epigenetic modifications that influence cellular processes such as covalent attachment of methyl or acetyl groups to lysine and arginine amino acids and the phosphorylation of serine or threonine. Phosphorylation at Thr3 of histone H3 is highly conserved among many species and is catalyzed by the kinase haspin. Immunostaining with Phospho-specific antibodies in mammalian cells reveals mitotic phosphorylation at Thr3 of H3 in prophase and its dephosphorylation during anaphase.
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