<p>Histone H4 is one of the four histones, along with H2A, H2B and H3, which form the eukaryotic nucleosome core. Along with H3, it plays a central role in nucleosome formation. The sequence of histone H4 has remained almost invariant in more then 2 billion years of evolution [<cite idref="PUB00004448"/>]. The signature pattern for this entry is a pentapeptide found in positions 14 to 18 of all H4 sequences. It contains a lysine residue which is often acetylated [<cite idref="PUB00003642"/>] and a histidine residue which is implicated in DNA-binding [<cite idref="PUB00004015"/>]. </p>