Histones are highly basic proteins that are abundant in lysine and arginine residues and are found in eukaryotic cell nuclei. They play a crucial role in the structure and organization of DNA in the nucleus. Histones act as spools around which DNA winds to create structural units called nucleosomes. There are five families of histones, which are designated H1/H5 (linker histones), H2, H3, and H4 (core histones) . The nucleosome core is formed of two H2A-H2B dimers and a H3-H4 tetramer. The tight wrapping of DNA around histones is a result of electrostatic attraction between the positively charged histones and negatively charged phosphate backbone of DNA.

Histones also play a role in the regulation of gene expression. Eight histone proteins can come together to make up something called a nucleosome, which is like a tiny spool that DNA can wind around. Histones can be marked in ways that are like open or closed signs for a business. If the histones near a gene have certain marks, open signs, they can tell us that in a particular cell were looking at a gene that is "on" — is open for business. If those histones have a different set of marks like a closed sign, those can tell us that in a particular cell a gene is "off," or closed for business. By studying histones and their marks, scientists have been able to learn a lot about what genes are turned on or off in different cell types.

In summary, histones are proteins that provide structural support for chromosomes and play a crucial role in the structure and organization of DNA in the nucleus. They are found in eukaryotic cell nuclei and act as spools around which DNA winds to create structural units called nucleosomes. Histones also play a role in the regulation of gene expression.