Nucleosomes are basis units of DNA packaging in eukaryotic cells. A core particle (mono-nucleosome) consists of a segment of DNA called core DNA (147 bp in length) wound around a histone octamer (Fig 1.). Histone octamers are made up of 2 copies of the the core histones H2A, H2B, H3, and H4. These mono-nucleosomes are connected by linker 80bp-long DNA. H1 histone, the so-called linker histone, binds to the linker DNA close to the entry and exit of the core DNA and is involved in chromatin compaction (Fig 1.).