Histones are basic nuclear proteins that are responsible for the nucleosome structure of the chromosomal fiber in eukaryotes. Nucleosomes consist of approximately 146 bp of DNA wrapped around a histone octamer composed of pairs of each of the four core histones (H2A, H2B, H3, and H4). The chromatin fibre is further compacted through the interaction of a linker histone, H1, with the DNA between the nucleosomes to form higher order chromatin structures.Covalent modifications of the canonical core histones, including acetylation, phosphorylation, methylation, and monoubiquitination are used to mark nucleosomes to create chromatin domains with a range of functions.