Studies of Nucleosome Structure

The nucleosome is the elementary DNA-protein unit responsible for the organization of chromatin (for review, see Kornberg 1977; McGhee and Felsenfeld 1980). Investigations in this laboratory have focused on elucidating the structure of the nucleosome at atomic resolution and determining how it is assembled in the higher-order structure of chromatin. Accounts of this work have been reported recently (Richmond et al. 1981; Klug 1982). In this paper we provide a brief summary of our present understanding of nucleosome structure at an overall resolution of about 20 Å. Our approach to obtaining crystals that are ordered to a resolution beyond 6 Å and our progress toward solving the current crystals at 7-Å resolution are also presented. The path of the DNA superhelix and the course of the double-helical backbones should be clearly visible in the electron density map at 7-Å resolution. On the basis of the available diffraction data, the individual...