Histone protein is composed of several basic amino acids. It is soluble in water, but insoluble in ammonium hydroxide. They do not coagulate in heat. It is located in the nucleus or chromosomes. Chromosomes contain histone proteins H1, H2, H3, H4 etc. Histones play an important role in gene expression. For example, arginine, lysine, nucleohistone, globin etc.