Asymmetries in the nucleosome core particle at 2.5 angstrom resolution

The 2.5 Angstrom X-ray crystal structure of the nucleosome core particle pr esented here provides significant additions to the understanding of the nuc leosome, the fundamental unit of chromatin structure. Extensions are made t o the structure of the N-terminal histone tails and details are provided on hydration and ion binding. The structure is composed of twofold symmetric molecules, native chicken histone octamer cores and the DNA palindrome, whi ch were expected to form a perfectly twofold symmetric nucleosome core part icle. In fact, the result is asymmetric owing to the binding of the DNA to the protein surface and to the packing of the particles in the crystal latt ice. An analysis is made of the asymmetries by comparisons both within the nucleosome core particle and to the structure of the histone octamer core o f the nucleosome.