ACTIVATION OF HEN ERYTHROCYTE DEOXYRIBONUCLEOPROTEIN

In heterokaryons formed by fusing hen erythrocytes with human HeLa cells the erythrocyte nucleus is reactivated and resumes RNA synthesis. At an early stage of this reactivation process, the deoxyribonucleoprotein (DNP) undergoes characteristic changes in its cytochemical properties. We have found that similar DNP-changes can also be induced in the nuclei of intact red cells or in the nuclei of red cell ghosts by washing and incubating in salt solutions or tissue culture media devoid of serum proteins. These changes are not induced if 0.05 % (w/v) of autologous, bovine or human serum proteins are added to these media. The DNP-changes are expressed as an increased ability of DNP to bind the basic dyes acridine orange and ethidium bromide, an altered Feulgen reactivity and a lowered stability of DNP to heat denaturation. In spite of these DNP-changes the dry mass and total UV-absorbancy of the nuclei remain unchanged by the experimental procedure. The DNP changes appear to be induced ny non-enzymatic reactions and to be highly dependent on such factors as adhesion of the cells to glass, cell-to-cell interaction, the ionic environment and the presence or absence of certain serum proteins in the medium. It is suggested that the DNP-changes reflect the existence of a chromatin activation reaction" which is essential for transforming inactive and highly condensed DNP and chromatin into active templates for RNA synthesis. This activation reaction may be intimately coupled to changes in the cell membranes and in the ionic environment surrounding the chromatin. © 1969."