On the structure of active chromatin. A flow linear dichroism study of chromatin fractionated by nuclease digestion

Nuclei from Ehrlich ascites cells were treated with micrococcal nuclease or DNase I and extracted with 1 mM EDTA. The chromatin fraction released by this procedure showed positive flow linear dichroism (LD) at low salt (2 mM NaCl) while the non-released fraction had negative LD. Furthermore, the chromatin structure responsible for the positive LD was found to be labile: The LD was reduced by heat (37 degrees C) or RNase treatment and inverted to a negative LD by electric fields (10 kV/cm) and by the presence of DNA binding dyes.