Discussion 183 



DISCUSSION 



Spiegelman : I wonder whether staphylococcal RNAse can break down 

 non-homologous RNA to active fragments. This could explain the 

 specificity of the intact RNA, i.e. the RNA is actually broken down in 

 those cases where it exhibits activity. Were this the case the specificity 

 would react with the enzyme, not the RNA. 



Gale: I cannot contradict that suggestion. I can only say that there 

 is no detectable RNAse activity in the disrupted cell preparation. 



Butler: I should like to mention results of some experiments by my 

 colleague Dr. Hunter, which were actually begun in Dr. Gale's labora- 

 tory. He found an inhibiting effect of some nitrogen mustards on the 

 incorporation phenomenon. This was with the intact bacterium under 

 starved conditions. He has got very good correlation between the 

 inhibition of incorporation and the inhibitory effect of these com- 

 pounds on the Walker tumour. But if the examination is done under 

 protein synthesis conditions there is no great inhibition, it is only found 

 under the cell exchange conditions. 



Pirie: What enzyme was it whose formation was inhibited by radi- 

 ation of the DNA preparation, and did you get inhibition with any lower 

 doses ? Did you find any physical changes in your preparation of DNA 

 after radiation with these doses? 



Gale: The enzyme was ^-galactosidase. I have not tested any other 

 enzyme system. I have concerned myself principally with amino acid 

 incorporation, where irradiation of the staphylococcal nucleic acids has 

 no effect on their ability to promote glycine incorporation. 



Cohn: This might be an appropriate time to make a few comments 

 on nucleic acids, and in making them I imply no criticism of any 

 particular work here or otherwise, but rather in the. light of more exact 

 interpretation of evidence which has been accumulated. There is no 

 doubt that nucleic acids and the deoxyribonucleic acids, polydiesters of 

 sugars and phosphates, do exist in tissue, and that they also exist in the 

 preparations that are made from tissues. But it is a long step from there 

 to assuming that the preparations that have been made (and this 

 applies to all the preparations of which I have any knowledge) are any- 

 where near as clean as the letters or the formulae used to represent them. 

 There is a great deal of doubt as to whether even crystalline proteins are 

 100 per cent what they are reputed to be, and certainly with respect 

 to such a characterization as crystallinity the nucleic acid field is far 

 removed. I think it was Gulland who said that "Nucleic acids are not 

 compounds, they are methods of preparation ". Now we know that there 

 are impurities in nucleic acid preparations, and no one has reported much 

 better than 90 per cent purity by any reliable means on any nucleic acid 

 preparation. If we overlook the possible biological significance of 5 or 

 10 per cent, we overlook all that we know about trace elements and trace 

 compounds such as enzymes. Furthermore, it is exceedingly difficult to 

 remove ribonuclease or ribonuclease-like enzymes from nucleic acid 

 preparations. Many nucleic acid preparations will autolyse themselves 

 if given a chance, showing symptoms of contamination with their own 



