BIOCHEMICAL PROPERTIES OF THE ISOLATED NUCLEUS I9I 



incorporation into such well dcfineil proteins as the arginine- and lysine-rich 

 histones is progressive with time. The relatively low uptakes into histone obtained 

 in these in vitro experiments agrees with earlier results obtained in vivo, in which 

 it was noted that the uptake of N'"' -glycine into the histones ot liver, pancreas 

 antl kidney is much lower than the uptake into the residual proteins of the 

 chromosome. The agreement between //; vivo and //; vitro studies is further sup- 

 port for the belief that amino acid uptake in isolated nuclei is an indication of 

 protein synthesis. 



ROLE OF DEOXYRIBONUCLEIC ACID IN PROTEIN SYNTHESIS 



The notion originally suggested by Brachet and Caspersson, that ribonucleic 

 acids play a role in protein synthesis, is now widely accepted as demonstrated. 

 Thus it has been shown that, in bacterial cell residues (13) and in liver micro- 

 somes (i, 19) ribonuclease acts to suppress amino acid incorporation. 



The isolated cell nucleus affords a unique opportunity to test the role of the 

 deoxyribonucleic acids in the process of protein synthesis and in other synthetic 

 systems, and the results have a special interest because they ultimately bear on 

 the function and mode of action of the gene, and on the chemical relationships 

 between the nucleus and the cytoplasm. 



A number of experiments relating DNA to protein synthesis in the nucleus have 

 been described (5, 6). These experiments deal with the efifects of treating nuclei 

 with crystalline pancreatic deoxyribonuclease (DNAase) on the nuclear capacity 

 for amino acid uptake. Briefly, when isolated nuclei are treated with DNAase 

 before adding C^* amino acids, the incorporation of the latter is markedly im- 

 paired. The degree of impairment becomes greater as more and more of the 

 DNA is depolymerized and removed from the nucleus. Experiments showing the 

 relationship between loss of DNA and inhibition of alanine-i-C-'^* and lysine-2-C^* 

 uptakes are summarized in figure 4. It is clear that removal of much of the DNA 

 seriously damages the capacity of the nucleus for subsequent protein synthesis. 

 It should also be pointed out that the sensitivity of the nucleus to treatment with 

 deoxyribonuclease is further evidence for the absence of appreciable whole cell 

 contamination, because intact cells are not sensitive to treatment with this enzyme. 

 Thymus tissue slices or minces, for example, show only a slight inhibition of 

 alanine-C^* uptake following treatment with DNAase, and the decrease observed 

 could easily be attributed to enzyme attack on cells which had been damaged 

 mechanically. 



The amino acid incorporating ability of nuclei is not irreversibly destroyed by 

 treatment with deoxyribonuclease. It was found that the addition of a DNA 

 supplement to nuclei depleted of their DNA would restore much of their capacity 

 for C^'' uptake (5). 



The most striking point about such 'restoration' experiments is the lack of 



