Fig. 8. Chemical Composition of Enzymatically Synthesized DNA with Different Primers, 



enzyme which transfers glucose from uridine diphosphate glucose directly and 

 specifically to certain HMC residues in the DNA (30). 



Chemical composition of enzymatically synthesized DNA. 

 The third line of evidence is supplied by an analysis of the purine and 

 pyrimidine base composition of the enzymatically synthesized DNA. We may 

 ask two questions. First, will the product have the equivalence of adenine 

 to thymine and of guanine to cytosine that characterize natural DNA? Sec- 

 ondly, will the composition of the natural DNA used as primer influence and 

 determine the composition of the product? In Fig. 8 are the results which 

 answer these two questions (31). The experiments are identical except that in 

 each case a different DNA primer was used: Mycobacterium phlei, Escherichia 

 coli, calf thymus and phage T2 DNA. In answer to the first question it is clear 

 that in the enzymatically synthesized DNA, adenine equals thymine and 

 guanine equals cytosine so that the purine content is in every case identical 

 to the pyrimidine. In answer to the second question it is again apparent that 

 the characteristic ratio of adenine-thymine pairs to guanine-cytosine pairs of 

 a given DNA primer is imposed rather faithfully on the product that is synthe- 

 sized. Whether these measurements are made with isotopic tracers when the 

 net DNA increase is only i % or if it is i 000 % the results are the same. It 

 can be said further that it has not been possible to distort these base ratios 

 by using widely differing molar concentrations of substrates or by any other 

 means. In the last line of Fig. 8 is a rather novel "DNA" which is synthesized 

 under conditions that I will not describe here (18, 32). Suffice it to say that 

 after very long lag periods a copolymer of deoxyadenylate and thymidylate 



s-60 



