DNA packaging becomes difficult to study without understanding the nucleosome.

It is visible under an electron microscope. Each bead is known as a nucleosome. The string depicts the DNA. Each nucleosome consists of eight proteins known as histones. Five types of histones include H1, H2A, H2B, H3, and H4. Hence, each nucleosome consists of four main histones, each two in number. These proteins form a barrel-shaped core octamer with a DNA string wound twice around the barrel.

The DNA linking the two nucleosomes is known as a linker DNA. The chromatin or a DNA histone complex gets stained with a suitable dye. The histones also contain large amounts of arginine and lysine.

The charge of the amino acids is positive. Hence, it facilitates an easy binding with a negatively charged DNA. Like linker DNA, vertebrates consist of linker histones such as H1 a-e, H10, H1t, and H5.

Each nucleosome gets attached to a linker histone acting like a clamp and preventing the coiled DNA from getting detached. Hence, the nucleosomes associate to form a 30nm fiber as revealed by the cell-breakage techniques. It involves interphase chromosomes in a highly condensed state or metaphase.