Nucleosomes are the basic repeating units of chromatin in which DNA is wrapped twice around a histone octamer consisting of two copies of each of the core histones, H2A, H2B, H3, and H4. Peripheral proteins, including the histone H1, interact with nucleosomes to affect chromatin structure. Histones undergo many modifications, which include acetylation, methylation, and phosphorylation, that are important for the regulation of gene transcription. Histone (calf thymus) consists of a mixture of H1, H2A, H2B, H3, and H4 histones isolated from calf thymus.
