CODE-SCRIPT OF BIOLOGICAL HIGH POLYMERS 123 



of deoxyribonucleic acid from mammalian tissue really com- 

 prises between 100,000 and 300,000 different individuals, the 

 isolation of "pure" compounds is unattainable; and it is even dif- 

 ficult to conceive of the criteria that would apply. For my part, I 

 must say that the significance of the existence of many deoxy- 

 ribonucleic acid fractions is by no means clear. There is still, I 

 believe, a great mystery hidden in the structure of the nucleic 

 acids. 



From much of what I have said before it must have been 

 evident how important it would be to gain an insight into the 

 order of alignment of the nucleotide monomers in a nucleic acid 

 chain; for the "information" coded into the nucleic acids must 

 find its chemical expression in the specific arrangement of the 

 purines and pyrimidines on the sugar phosphate backbone, that 

 is, in the nucleotide sequence. I have no time here to discuss our 

 earUer attempts, such as the stepwise enzymic degradation or the 

 study of the formation and the breakdown of the apurinic acids^^, 

 which had served to emphasize the arrhythmic character of the 

 polynucleotide chain. But I should like to say a few words about 

 the results of our recent work which is based on the method of 

 differential distribution analysis developed with Shapiro-^. This 

 procedure, which consists in the analysis of the breakdown 

 products formed by the controlled, stepwise acid degradation of 

 deoxyribonucleic acids, makes use of the great lability towards 

 acid of the purine glycosides. If we consider a segment of a 

 polynucleotide chain, we may assume that it will contain 

 "solitary" pyrimidine nucleotides flanked by purine nucleotides 

 and vice versa as well as "bunched" stretches of varying length 

 consisting exclusively of purine or of pyrimidine nucleotides 

 (compare Fig. 8, p. 90). The first stage of acid degradation, to 

 which we shall limit ourselves today, results in the removal of 

 the purines followed by chain rupture in such a manner as to 

 liberate the "solitary" pyrimidine nucleotides in the form of the 

 nucleoside 3 ',5 '-diphosphates. These, as well as other more com- 

 plex breakdown products, can be determined quantitatively, 

 furnishing a characteristic feature of the particular deoxyribonu- 



References p. 125 



