Histone tails. Two views of histone N-terminal tails protruding from between the two DNA duplexes that supercoil around the nucleosome. (a) Ribbon representation, looking at the circular face of the nucleosome. (b) Space-filling representation of the nucleosome as viewed from the side. Some tails pass between the supercoils through holes formed by alignment of the minor grooves of adjacent helices. The H3 and H2B tails emerge between the DNA turns wrapped around the histone; the H4 and H2A tails emerge between adjacent histone cores.