STEPWISE REMOVAL OF HISTONES FROM NATIVE DEOXYRIBONUCLEOPROTEIN BY TITRATION WITH ACID AT LOW TEMPERATURE AND SOME PROPERTIES OF RESULTING PARTIAL NUCLEOPROTEINS

Stepwise removal of histones from deoxyribonucleoprotein by titration with acid at about -1 °C was essentially the same as that found previously at 2 to 5 °C. This was established from the amino acid composition and the behaviour on ionexchange chromatography and zone electrophoresis of the histones removed. Sedimentation and spectrophotometric measurements on the deoxyribonucleoprotein remaining after titration to various low pH values (i.e. the partial deoxyribonucleoproteins) showed that the material was macromolecular and had retained its hypochromicity; thus the DNA of the partial deoxyribonucleoproteins was not appreciably depurinated or denatured during titration. Removal of histones from native deoxyribonucleoprotein was accompanied by a drop in melting temperature and sedimentation rate, by an increase in susceptibility to hydrolysis by pancreatic deoxyribonuclease, and by an improved efficiency in the support of RNA synthesis by the polymerase of Escherichia coli. Attempts have been made to use partial deoxyribonucleoproteins in studies of some aspects of the structure of native deoxyribonucleoprotein. The most reasonable interpretation of the results suggests a structure involving a distribution of the different histones along polynucleotide chains which is intermediate between the extremes of long regions of polynucleotide covered with only one type of histone, and a distribution where no two like histones are adjacent. © 1969.