What is the structure of histones?

Histones are composed of a tail and an amino acid chain that consists of three specific domains. Among these domains, only the central one is made up in a folded conformation and is approximately 80 residues long. This is known as the histone fold domain, which is created by the arrangement of three α-helices linked by two loops. There are five main types of histones: H1, H2A, H2B, H3, and H4. The core histones (H2A, H2B, H3, and H4) are characterized by the histone fold domain. These core histones form an octamer structure (two copies of each H2A, H2B, H3, and H4) known as a histone octamer. DNA wraps around this histone octamer to form nucleosomes, which are the basic units of chromatin structure. The linker histone H1 is involved in linking nucleosomes together. Histones also have high levels of lysine and arginine residue, which interact with the negatively charged phosphate groups of DNA. This allows them to bind to DNA and help in its packaging and condensation within the nucleus.