74 Information Storage and Neural Control 



Until this is done, it will not be possible to study the effects of 

 specific agents on the RNA and on the resulting proteins. The 

 only kinds of messenger RNA's which are available are the syn- 

 thetic ones. 



James E. Darnell, Jr. (Cambridge, Massachusetts): The viral 

 RNA's were the first to be treated with deaminating agents. 

 Schuster's work with tobacco mosaic virus (TMV), which showed 

 that deamination of cytosine resulted in mutation, confirmed the 

 fact that the chemical change is preserved in the progeny particles. 

 The deamination, which results in mutation of TMV particles 

 and change in the protein code, is assumed to be preserved from the 

 initial change in the RNA of the virus. If one considers viral 

 RNA's as messengers, which they are, then this type of messenger, 

 at least, can be treated with mutagens, and the residual damage, 

 if you will, can be preserved. 



Echols: I suppose I am being unfair to the viral RNA's, although 

 it has not been clearly established that the viral RNA functions 

 directly as a messenger. 



Heather D. Mayor (Houston, Texas): There are clear in- 

 dications from viral RNA that the seat of genetic information 

 can be RNA as well as DNA. I think there is quite good evidence 

 that an RNA virus can act as its own messenger. I should like to 

 ask Dr. Echols if he has any information from mutations on closely 

 positioned bases in DNA. Is there any evidence that the code is 

 indeed a triplet sequence rather than, say, a multiple of six? In 

 fact, are there any data indicating that six bases could represent 

 the fundamental unit of the code? 



Echols: I think that there is no compelling evidence, even 

 taking Crick's work into consideration, defining the size of the 

 coding unit. However, the work of Nirenberg and Ochoa cer- 

 tainly suggests that the number of bases which code an amino 

 acid cannot be an exceedingly large number. If a large number 

 were required, the only thing which should promote incorporation 

 of most amino acids would be a polymer containing all four bases. 



Mayor: If you have four bases and a triplet code, you could 

 possibly get codes for sixty-four different amino acids instead of 

 the twenty we know to be involved. Do you think that dif- 

 ferent combinations of bases may code the same amino acids? 



