MUTAGENESIS 



95 



Neel: Are you postulating, then, that bromouracil has properties 

 such that no matter what its original pairing, it is by reason of its 

 chemical structure more apt to pair with the alternate possibility than 

 the normal molecule would in that position? 



Freese: That's right. Actually, it is not only able to make this mis- 

 take more frequently than thymine, but more frequently than the 

 whole background of spontaneous mutations. Figure 18 shows 



2- aminopurine 

 (normal amino-state) 



thymine 

 (normal keto-stote) 



adenine 

 (normal amino-state) 



thymine 

 (normal keto-state) 



Figure 18. 



