Histones are the core components of the nucleosomes that wrap and compact DNA into chromatin. DNA compacting limits accessibility to the cellular machineries which require DNA as template. Histones play a central role in transcription regulation, DNA repair, DNA replication and chromosomal stability. The accessibility of DNA is regulated by post-translational modifications of histones such as acetylation,Mouse,ethylation and phosphorylation. The nucleosome is a histone octamer containing two molecules each of histone proteins H2A, H2Bovine, H3 and H4 assembled in one H3-H4 heterotetramer and two H2A-H2B heterodimers.