DEOXYPENTOSE NUCLEIC ACIDS 31 



of calf thymus DNA^^ had shown it to proceed according to a 

 peculiar and complex pattern. The action of the enzyme resulted 

 in the formation of dialyzable fragments and of a dialysis residue 

 (core). The latter was characterized by greatly increased ratios 

 of adenine to guanine, thymine to cytosine, purines to pyrimi- 

 dines, and by greater resistance to enzymic attack. Preliminary 

 results of studies of this type on wheat germ DNA are presented 

 in Table 12. The analytical findings on the intact DNA are in 

 good agreement with analyses recently reported for the same 

 nucleic acid from two other laboratories^^- ^^. The figures given 

 here for the "19% core" and the "8% core" refer to the dialysis 

 residues recovered when 81 and 92% of the DNA respectively 

 had been converted by the enzyme to dialyzable fragments. The 

 trend of degradation appears similar to that observed with calf 

 thymus DNA. 



The molar ratios found in the DNA specimens studied in our 

 laboratory are compared in Table 13. The tendency toward 

 certain regularities will be observed. The figures for hen DNA 

 (chicken erythrocytes) and for the DNA from the K-12 strain of 

 E. coli must be considered as preliminary. Both components were 

 studied in collaboration with B. Gandelman. The DNA of 

 Hemophilus influenzae, type c, was studied by S. Zamenhof. A 

 few points are noteworthy. In the case of wheat germ DNA, 

 methylcytosine and cytosine apparently must be considered 

 together, if the regular ratios, observed in most other instances, 

 are to be obtained. Another remarkable fact is that the regu- 

 larities are maintained even in the nucleic acids of the "GC type" 

 despite the complete inversion in individual ratios. 



As was already mentioned before, it is almost impossible to 

 decide at present whether these regularities are entirely fortuitous 

 or whether they reflect the existence in all DNA preparations of 

 certain common structural principles, irrespective of far-reaching 

 differences in their individual composition and the absence of an 

 easily recognizable periodicity. It may be assumed that the 

 nucleic acids as we know them today, as for that matter also the 

 proteins, are the result of an age-long selection process in the 



References p. 37 



