Explanation

Histones are a set of positively-charged, basic proteins. Histones are rich in the basic amino acid residuesl lysines and arginines. Both the amino acid residues carry positive charges in their side chains. Two molecules of each of the four types of histones – $H_{2}A,\ H_{2}B,\ H_{3}\ and\ H_{4}$ are organized to form histone octamers. These form the inner core of nucleosome. The negatively charged DNA is wrapped around the positively – charged histone octamer to form a structure called nucleosome.