X-RAY-DIFFRACTION ANALYSIS OF CRYSTALS CONTAINING TWOFOLD SYMMETRICALNUCLEOSOME CORE PARTICLES

Nucleosome core particles containing a DNA palindrome and purified chi cken erythrocyte histone octamer have been reconstituted and crystalli zed. The dyad symmetry of the palindrome extends the dyad symmetry of the histone octamer to result in a twofold symmetric particle. This en sures that the structure determined by X-ray diffraction will yield a true representation of the DNA strand rather than the twofold averaged structure which would result from using a non-palindromic DNA sequenc e. The crystals provide isotropic diffraction to 3.2 Angstrom with obs erved reflections extending to d spacings of about 2.8 Angstrom using a rotating-anode CuK alpha X-ray source. Although the DNA palindrome i s a factor contributing to the quality of the diffraction data, anothe r significant factor is an improved preparative technique which enrich es for correctly phased nucleosome core particles.