82 Informatio7i Storage and Neural Control 



Two stages of degradation follow: 7-alkylguanine splits off, and 

 a slow fission of the sugar phosphate chain follows (41). If in the 

 process of replication of the DNA which has been exposed to 

 nitrogen mustard, the guanine of the template is skipped, the 

 resulting sequence of nucleotide bases in the daughter chain will 

 be altered. Another mutagen which apparently acts by deleting 

 a base from the DNA chain is proflavin, an acridine derivative, 

 A series of T-4 bacteriophage mutants induced by proflavin have 

 been studied by Crick et al. (13). The mutants in almost all cases 

 manifest a complete inactivation of the function of the eene 



Equations 1 through 3 depict schematically some current ideas 

 about genetic coding (13): 



(TRIPLET) 



I ' I II 1 I 1 I 1 I 1 I 1 



[1] TGCTGCTGGTGCTGGTGGTGA--- 



I - ' — '-I— I— 1 — 1— I — l-_l_l_l_l_l_l_l_l_|_|__L I 

 Starting ' 



point Normal DNA Ghain 



I I I 1 I 1 1 1 r 



"1 r 



[2] TGGTGTTGGTGGTGGTGGTGA - 



I — I — I — I — l^-l I I I I I ^1 L_l l_l__l_L_l._[ 



Starting: T 



^iD 



point Gonversion of G to T by Nitrous Acid 



(Gene may still be functional, amino acid in 

 protein chain is changed). 



[3]TGGTGTGGTGGTGGTGGTGA 



I — ' — I— I— I— 1^1 I I I L_l I I l_I_^l_^l__I_| 



Starting T 



point G deleted from Ghain by Proflavin or Nitrooen 



Mustard 



(Gene inactivated). 



It is assumed that a triplet of three nucleotide bases (for example, 

 TGG) codes each particular amino acid in the protein chain. It is 

 further assumed that the DNA chain is translated from a fixed 

 starting point and that the genetic code is nonover lap ping. If one base 

 in the chain is altered (for example, the change of G in the second 



