Dissociation de la nucléoprotéine d'érythrocytes de poulets par les sels

Abstract

The dissociation by NaCl of the nucleoprotein of chicken erythrocytes (histone/DNA = 1.2, acid protein/DNA = 0.24) has been systematically studied. The proteins dissociated at different ionic strength were characterized by amino-acid analysis and disc electrophoresis. The lysine-rich histone fraction is dissociated first by μ= 0.4–0.5, the erythrocyte-specific histone fraction a little later by μ= 0.6–0.7. Above μ= 0.7 there is no further selectivity of dissociation. Up to an ionic strength of μ= 0.3 there is practically no liberation of protein, then to μ= 0.7 such liberation is linear. Between μ= 0.7 and μ= 1.0 the curve representing the quantity of histone liberated as a function of the ionic strength presents sections of different slope, indicating that the dissociation of histones occurs by successive stages in this region of ionic strength. Between μ= 1.0 and μ= 2.0 the slope of the curve decreases continuously; at μ= 2.0 the slope becomes essentially zero, indicating that histone dissociation is complete. A method for the preparation of the lysine-rich fraction and of the erythrocyte-specific fraction is proposed. A large percentage of nucleoprotein is precipitated by salt at ionic strength up to μ= 0.6. At higher strength the nucleoprotein is redissolved progressively and the study of the residual complex is possible. The denaturation curves of the residual complexes obtained by dissociation of the nucleoprotein at these ionic strengths present two transitions, suggesting a heterogeneity of sites on the nucleoprotein molecule after dissociation by salt.