The isolation and properties of deoxyribonucleoprotein particles containing single nucleic acid molecules

Abstract

Summary A gel-free solution of deoxyribonucleoprotein was prepared in high yield from calf thymus by maintaining the concentration and ionic strength at very low values and by careful homogenization. The resulting material was examined by a number of different macromolecular methods and found to consist of completely dispersed deoxyribonucleoprotein particles of high asymmetry and containing nearly equal amounts of deoxyribonucleic acid and protein. The molecular weight determined by light scattering was 18·5 million. Upon dissociation the deoxyribonucleic acid obtained had a molecular weight of 8 million suggesting that the deoxyribonucleoprotein particles consisted essentially of one deoxyribonucleic acid molecule and a nearly equal amount of protein. Hydrodynamic investigations and direct electron microscopic examination indicate that the protein is rather evenly distributed along deoxyribonucleic acid chains. Optical rotatory dispersion and infrared spectral studies, while ambiguous, do suggest that a major part of the protein is in the a-helical configuration. It is shown that a large fraction of the histone can be accommodated in sections having the α-helical configuration in the large groove of the double-stranded deoxyribonucleic acid helix and that such a model is consistent with the observations made thus far.