Histone H4 is one of the five main histone proteins involved in the structure of chromatin in eukaryotic cells. Featuring a main globular domain and a long N-terminal tail, H4 is involved with the structure of the nucleosome of the 'beads on a string' organization. Histone H4 is an important protein in the structure and function of chromatin, where its sequence variants and variable modification states are thought to play a role in the dynamic and long term regulation of genes.