Abstract
Histones are the protein components of the nucleosome, which forms the basic architecture of eukaryotic chromatin. Histones H2A, H2B, H3, and H4 are composed of two common regions, the “histone fold” and the “histone tail”. Many efforts have been focused on the mechanisms by which the post-translational modifications of histone tails regulate the higher-order chromatin architecture. On the other hand, previous biochemical studies have suggested that histone tails also affect the structure and stability of the nucleosome core particle itself. However, the precise contributions of each histone tail are unclear. In the present study, we determined the crystal structures of four mutant nucleosomes, in which one of the four histones, H2A, H2B, H3, or H4, lacked the N-terminal tail. We found that the deletion of the H2B or H3 N-terminal tail affected histone–DNA interactions and substantially decreased nucleosome stability. These findings provide important information for understanding the complex roles of histone tails in regulating chromatin structure.
Highlights
The basic unit of chromatin is the nucleosome core particle, which contains 145–147 base pairs of DNA [1,2,3]
We bacterially expressed and purified four histone mutants, which lacked the N-terminal 9, 24, 27, and 15 amino acid residues of H2A, H2B, H3, and H4, respectively (Fig. 1(A) and (C)). These truncated N-terminal regions of the histones contain many previously identified post-translational modification sites [26,39]. These deletion mutants were designed based on the tailless histones obtained by the trypsin protease treatment [40], and the previous crystal structures of nucleosomes (Fig. 1(B)) [1,28,30,41]
Reconstitution was performed by the salt dialysis method [28,30], and the nucleosomes were purified by native polyacrylamide gel electrophoresis using a Prep Cell apparatus [29]
Summary
The basic unit of chromatin is the nucleosome core particle, which contains 145–147 base pairs of DNA [1,2,3]. The N-terminal tails of the four core histones and the C-terminal tail of histone H2A protrude from the nucleosome core particle [2]. The histone tails contact the DNA wrapped around the histone octamer, and bind to linker DNA [7] and the acidic patches of the neighboring nucleosomes [1,2,8]. These interactions between histone tails and DNA may play critical roles in the formation of higher-order chromatin.
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