-78 ERWIN CHARGAFF 



The investigation of the deoxyribonucleic acid of rye germ [37] offered 

 us, for the first time, the opportunity of comparing the pyrimidine distri- 

 bution in the total preparation with that found in a complete series of 

 seven fractions isolated through the fractional dissociation of the histone 

 nucleate. These fractions were, in their distribution and composition, 

 remarkably similar to those previously isolated by the fractionation of the 

 deoxyribonucleic acid from wheat germ [38]. The availability of such a 

 complete series of fractions permitted, moreover, a test of the validity of 

 the results given by the difi^erential distribution analysis; a weighted 



TABLE III 



Composition of Deoxyribonucleic Acids of Rye Germ and Wheat Germ 



* Taken from a previous publication [37]. 

 f Taken from a previous publication [38]. 



average of the values recorded for the individual fractions could be com- 

 pared with those given by the total nucleic acid preparation that had not 

 been subjected to fractionation and showed an excellent agreement [37]. 



The principal results of this study are, as regards the frequency of 

 solitary pyrimidine nucleotides, shown schematically in Fig. 2. In this 

 histogram, we give a brief description of the total pyrimidine composition 

 of all specimens examined — total deoxyribonucleic acid and seven fractions 

 — and depict the quantities of solitary nucleotide of each of the three 

 pyrimidines as per cent of the total constituent in the preparation. 5- 

 Methylcytosine, it will be seen, has a surprisingly high tendency, when 

 compared with the other 6-aminopyrimidine, cytosine, to occur as a 

 solitary unit, similar in this respect to thymine. I shall return to this point 

 later. 



