Histones are proteins that package DNA into nucleosomes. Histones are responsible for maintaining the shape and structure of a nucleosome. One chromatin molecule is composed of at least one of each core histones per 100 base pairs of DNA. During chromatin-regulated processes, histone H2A combines with Histone H2B to form the H2A/H2B heterodimer. The histone H2A-H2B heterodimer functions dynamically in and out of the nucleosome.