194 



SUBCELLULAR PARTICLES 



Table 4. Effect of ribonucleosides, nucleotides and dinucleotides on c -alanine uptake 



by dnaasc-treated nuclei 



* Nucleoside 2' and 3' phosphates. t Nucleoside 5' phosphates. 



and molecular size emerges as one of the factors which determines whether a 

 compound will substitute for DNA in restoring amino acid uptake to DNA-de- 

 pleted nuclei. 



Among other factors which determine the capacity of a polyelectrolyte to substi- 

 tute for DNA is its electrical charge. Polycations, such as polylysine or protamine, 

 which carry a net positive charge at neutral pH values, cannot restore function. 

 On the contrary, the addition of polylysine to 'control' nuclei which still retain 

 their original DNA content, markedly inhibits amino acid incorporation into 

 nuclear protein. The findings suggest that there is a correlation between negative 

 charge and the biochemical activity of the nucleus. Further tests of this hypothesis 

 are now in progress. If it is sustained, it may be possible to demonstrate that one 

 role of the basic proteins (histones and protamines) in the organization of the 

 chromosome is to reduce or control chromosome function by masking the nega- 

 tive charges of the DNA. 



It may be mentioned in passing that 'neutral' proteins, such as serum albumin, 

 serum globulin or mixed plasma proteins, have no effect on amino acid uptake 

 by DNAase-treated nuclei. 



NUCLEAR ATP SYNTHESIS AND ITS RELATION TO PROTEIN SYNTHESIS 



Isolated nuclei prepared from calf thymus have been shown to be capable of 

 phosphorylating the AMP which they contain to form ADP and ATP (5, 20). 

 This process differs in several important respects from the type of oxidative phos- 



