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CHANGES IN NUCLEIC ACID METABOLISM 

 AS A RESULT OF RADIATION 



Charles E. Carter 



After discussing the effect of radiation on nucleic acids for over two 

 days, there is little left to be said about this subject. Nevertheless, I will try 

 to pick up a couple of loose threads. These remarks will be confined largely to 

 three aspects of the problem: (1) the effect of radiation upon the metabolism of 

 nucleic acids delineated through the incorporation of isotopic precursors into 

 desoxyribose nucleic acid; (2) the effect of radiation upon the structure of nu- 

 cleic acids; (3) the effect of radiation upon activity or specific function of the 

 nucleic acid insofar as we know it. 



In the first two of these categories our knowledge is approaching a 

 satisfactory state of affairs. In the last category, that of function or specific 

 biological activity, we cling to data that are provided by the cytogeneticists and 

 to the studies of bacterial transforming activity of high molecular weight desoxy- 

 ribose nucleic acid preparations. Obviously, this is the area in which knowledge 

 of nucleic acid biochenaistry is deficient. 



There is one fact I think we might establish before we get started that 

 imposes a limitation upon us. I think it can be stated this way: At this time Ido 

 not believe that any one of us is certain of the molecular identity of a nucleic 

 acid. Is that right. Dr. Chargaff? Do you know that you have a molecular spe- 

 cies when you work with a nucleic acid? 



CHARGAFF: There you come to the definition of a macromolecule. 

 What you really can't tell is what you mean by molecular weight of a protein. 

 The same thing goes for nucleic acid. But you are correct. One can't be sure. 



CARTER: This should not be an obstacle to research, rather, it 

 should promote it. But nevertheless I think that we should admit that limitation. 



First, we will discuss certain types of experiments that have employed 

 low molecular weight isotopic precursors to provide a matrix for discussion of 

 the problem of the metabolism of nucleic acid and how it is influenced by radia- 

 tion. 



I want to introduce this by a brief comment upon some of the assump- 

 tions that are made in this type of experimentation. Again, you can be so crit- 



