DIFFERENTIAL DISTRIBUTION ANALYSIS 139 



tain a fifth nitrogenous constituent, 5-methylcytosine, in appreci- 

 able quantity^' -^. In the specimens isolated from both wheat and 

 rye germ the concentration of this pyrimidine amounts to 5.9 

 mole % (Table 30). This means that nearly a quarter of the 

 cytosine has been "replaced" by methylcytosine. Since the molar 

 concentration of guanine equals the sum of these two pyrimidines, 

 one may consider them as pleromeric in the sense defined above. 

 Minor constituents of deoxyribonucleic acid (or, for that matter, 

 of ribonucleic acid) are destined to play an important role in 

 future work on the elucidation of nucleic acid structure, as they 

 will serve as additional markers in the array of nucleotides con- 

 stituting the polymer chain. Furthermore, the presence of a pyri- 

 midine sharing with cytosine the property of being a 6-amino 

 derivative and with thymine that of being a 5-methylpyrimidine 

 is of the greatest interest for a better understanding of the 

 mechanisms of selection, incorporation, and replication that are 

 at work. 



TABLE 30 



COMPOSITION OF DEOXYRIBONUCLEIC ACIDS OF RYE GERM AND WHEAT GERM 



* Taken from a previous publications^. 

 ** Taken from a previous publication's. 



References p. 159 



