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VINCENT G. ALLFREY 



'DNA lOmg/ml. 

 ,x Control 



DNA lOmg/ml 

 Histone lOmg/ml 



X Histone 10 mg/ml. 



20 40 

 Time (min) 



Fig. 9. Effects of added histone, DNA + histone, and DNA on [i-^^C]- 

 leucine incorporation into the proteins of isolated nuclear ribosomes. The specific 

 activity of the ribosomal protein (in cp-m./mg-) is plotted against the time of 

 incubation at 37°. 



500 



400 



>r 300 



Serunn albumin 



L-lys[ne___ 



U 



200- 



100 



CONTROL 

 Thymus histone 11 



rotamne 



Thymus histone I 



12 3 4 



Milligrams added 

 Fig. 10. Effects of added histone I (arginine-rich histone fraction), histone II 

 (lysine-rich histone fraction which is less basic than histone I), protamine, and 

 polylysine on [i-^*C]-alanine uptake into the proteins of isolated calf thymus 

 nuclei. The specific activity of the nuclear protein after 60 min. incubation at 37° 

 is plotted against the amount of material added to the nuclear suspension. 



DNA or histone at different loci of the chromosome. This may prove to be 

 a physiological mechanism for controlling the rates of synthesis of different 

 proteins in the nucleus, and one may speculate that such control is part 

 of the process of cell differentiation. 



