48 DEOXYPENTOSE NUCLEOPROTEINS AND PROSTHETIC GROUPS 



solutions of MgCb alone are employed, the liberation of nucleic 

 acid from its complex with histone occurs at even lower salt 

 concentrations, as much as 70% of the nucleic acid P being 

 detached by 0.3 M MgClo and almost the entire amount by a 

 0.6 M solution. 



Fig. 5. Effect of magnesium ions on the fractional dissociation, in the 

 presence of a CHCI3 phase, of artificial histone complexes with calf 

 thymus deoxyribonucleic acid. The weight ratio of histone to nucleic acid 

 P was 17. The successive extractions were performed with NaCl solutions 

 of the indicated molarity in the absence (curve 1) and in the presence of 

 0.06 M MgCl2 (curve 2). Co-ordinates as in Fig. 2. (Taken from Cramp- 

 ton et al.^.) 



In these experiments the histone nucleate complex was formed 

 at the lowest NaCl concentration employed for fractionation. The 

 conditions under which the complex is formed are, however, not 

 without influence on its subsequent behavior. This is brought 

 out by the experiments assembled in Fig. 6. Two differently 

 treated nucleohistone preparations are compared in curves 1 and 

 2. Before being precipitated by dialysis against 0.15 M NaCl, one 

 portion was in contact with 3 M NaCl (curve 2), the other portion 

 remained in distilled water (curve 1). The precipitates then were 

 extracted successively with salt solutions of increasing strength 

 in the absence of a denaturing chloroform phase. Similarly, 

 artificial histone nucleates were formed in the absence of salt 



