a group of proteins weakly exhibiting the characteristics of bases. Histones are classified as simple proteins. They are contained in the nuclei of the majority of cells in animals. The proteins of erythrocytes and the thymus gland are particularly rich in histones. The alkaline properties of histones result from the presence of the basic amino acids—histidine, lysine, and arginine. Unlike the majority of proteins, histones contain almost no tryptophan. The molecular weight of histones ranges from 5,000 to 37,000. In the cell nuclei (particularly in the chromosomes), histones form a complex with deoxyribonucleic acid (DNA)—nucleohistone. It is thought that the joining of histones to DNA and their breaking away regulates the synthesis of ribonucleic acid (RNA) and hence the biosynthesis of proteins.