Reconstitution of compact polynucleosomes and comparison of the functions of histones H1 and H5.

Polynucleosomes with a definite length (about 4,500 base pairs) were prepared from chicken erythrocyte nuclei without depleting magnesium ions from the medium. The polynucleosomes in the presence of Mg2+ ions as well as monovalent salts were more compact than those with monovalent salts alone. We minimized the occurrence of nicks in the DNA of nucleosome fiber during the preparation. When histones H1 and H5 were completely removed from polynucleosomes, linker histone-depleted polynucleosomes sedimented slower than the original ones. When isolated histone H1 or H5 was reassembled with linker histone-depleted polynucleosomes, no significant difference was observed among the reconstituted polynucleosomes with histone H1, the reconstituted polynucleosomes with histone H5, and the original polynucleosomes. We concluded that histones H1 and H5 are similar in their effects on higher order structure of polynucleosomes, as far as can be judged from such characteristics as sedimentation velocity, linker histone content, and the patterns of nuclease digestion.