326 



CHAPTER 35 



H 

 Thymine 



o 



HN 



N 

 H 

 Uracil 



NH9 



NH 



NH, 



H 

 5-Methyl cytosine 



5-Bromo cytosine 



HN 



NH, 



FIGURE 35-5. Unnatural and common 

 natural bases utilized in in vitro synthe- 

 sis of DMA. Arrows point to groups 

 capable of typical H -bonding. 



in the primer is reproduced faithfully in the 

 synthesized product (see Figure 8 in Supple- 

 ment VI). In other words, in this respect the 

 product is a replica of the primer. This is 

 illustrated strikingly by the following experi- 

 ment. After a long period of incubation of 

 all the usual components except primer, a 

 linear deoxyribotide polymer composed only 

 of A and T is formed spontaneously. If this 



polymer is then used as the primer, even 

 though all four usual triphosphates are 

 present in the substrate, there is an extensive 

 synthesis of material which contains A and T 

 only, and has no trace of C and G (see again 

 Figure 8 in Supplement VI). 



It has been mentioned that for each nucleo- 

 tide added to the end of the DNA chain an 

 inorganic pyrophosphate is liberated. It has 



