Structural studies of the nucleosome core particle

The 2.5 Å X-ray crystal structure of the nucleosome core particle presented here pro- vides significant additions to the understanding of the nucleosome, the fundamental unit of chromatin structure. Extensions are made to the structure of the N-terminal histone tails and details provided on hydration and ion binding. The structure is com- posed of 2-fold symmetric molecules, native chicken histone octamer, and the DNA palindrome, which were expected to form a perfectly 2-fold symmetric nucleosome core particle. In fact, the result is asymmetric due to the binding of the DNA to the protein surface and to the packing of the particles in the crystal lattice. An analysis is made of the asymmetries by comparisons both within the nucleosome core particle and to the structure of the histone octamer core of the nucleosome.

Details of the discovery and investigation of macromolecular crystal annealing, M-CA, are also presented. This discovery was a direct consequence of studies directed toward obtaining high-resolution diffraction from nucleosome core particle crystals.

The existence of the phenomenon was completely unexpected and thus no documenta- tion of its mechanism or application to macromolecular crystals was available. MCA has already proven to be an important contribution to the field of macromolecular cryocrystallography.

Research sponsored by grants from NIH (GM-29818), NASA (NAG8-1568), the Office of Biological and Environmental Research, U.S Department of Energy, and the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy under Contract No. DE-AC05-00OR22725.