198 



SUBCELLULAR PARTICLES 



Table 6. Effect of polynucleotides on atp synthesis by DNAase-TREATED nuclei 



results are summarized in figure 5C and in table 6. It is evident that a DNA 

 supplement restores much of the nuclear capacity for ATP synthesis. 



It is of interest that mononucleotides are not extracted from the nucleus when 

 the DNA is removed. This retention of mononucleotides is in accord with previ- 

 ous observations which show that neither the histone nor the ribonucleic acid 

 contents of the nucleus are appreciably diminished by DNAase treatment (6). 



Subsequent tests of ATP synthesis in DNA-depleted nuclei showed that the 

 ability to phosphorylate AMP can be restored to nuclei by polynucleotides other 

 than DNA. Figure 5D shows the results obtained when one adds a supplement 

 of yeast RNA. (In other experiments, mentioned below in the discussion, it has 

 been found that other polyanions of non-nucleotide nature will also restore this 

 synthetic ability.) 



The question now arises as to how DNA and other polynucleotides play a role 

 in nuclear ATP synthesis. A number of possible mechanisms might be suggested 

 which utilize the relatively high energy of the internucleotide linkage. For exam- 

 ple, the reversibility of the ADP^polyadenylic acid reaction (catalyzed by poly- 

 nucleotide phosphorylase ( 14) ) suggests one way in which such energy could be 

 utilized. Experiments which will not be described in detail here have made such 

 phosphorylysis mechanisms very improbable, and also make it rather unlikely 

 that ATP synthesis involves the formation of an intermediate complex with nu- 

 clear DNA. Any consideration of the mechanisin of ATP synthesis in isolated 

 nuclei should begin with the observation that it is essentially coupled to oxidative 

 processes. This is shown most directly by the results of the following experi- 

 ment (2). 



Thymus nuclei were treated with DNAase, centrifuged, and resuspended in 



