Structure of Chromatin DNA not Complexed with Protein

Abstract

Rat liver chromatin was titrated by poly-D-lysine of mol.wt. 140,000. Approximately 32% of the phosphate groups of the chromatin were found to react with the polycation. By submitting the chromatin-poly-D-lysine complex to pronase and DNase I digestion and by further submitting the obtained DNA-lysine complex to hydroxy-apatite-chromatography, “free” DNA was isolated. The mean S-value of this DNA was found to be 10±0.8, corresponding to approximately 2100 nucleotide pairs, its renaturation kinetics similar to total DNA. On the basis of these results and on the findings that histone-saturated DNA-histone recombinates are digested with DNase I up to 65% a model of chromatin structure was proposed, taking into account protein covered- and free DNA regions. © 1974, Verlag der Zeitschrift für Naturforschung. All rights reserved.