31. SYNTHESIS OF POLYNUCLEOTIDES 143 



which is induced as a consequence of T-even phage infection. It should be 

 noted that this substitution or alteration of a pyrimidine moiety at poly- 

 nucleotide level is the first report of its kind. All other interconversions and 

 transformations of the polynucleotide constituents have hitherto been 

 found to occur at the monomeric level. 



Intriguing are the observations 96 made on polymerase assays in extracts 

 of E. coli after T2 phage infection. When assayed with "native" calf thymus 

 or T2 phage DNA as the primer, the amounts of the polymerase found in 

 normal and infected cells were found to be similar. However, a twelvefold 

 increase of the enzyme in the infected cells was found when DNA previ- 

 ously heated at pH 9 was used as the primer. Thus, it is not clear whether 

 infection results in the formation of a new type of polymerase or in an in- 

 crease of the normal polymerase with new factors governing its action. As 

 mentioned above, the polymerase from the infected cells can utilize the 

 normal cell DNA as the primer. However, since the DNA synthesized after 

 infection has the base composition of T2 phage DNA, it must be assumed 

 that the injected phage DNA somehow becomes the chosen primer for syn- 

 thesis after infection. Seen in a different way, the phenomenon may be 

 explained by assuming that the nuclease which has been found to increase 104 * 

 on phage infection destroys selectively in some manner the intrabacterial 

 DXA. (The steady decomposition of bacterial DNA on phage infection 

 had been reported upon previously by Hershey and co-workers. 95 ) 



The work described above may be regarded as being at an initial phase 

 but clearly opens up vistas of investigations, at the enzymic level, of com- 

 plex phenomena. Much more will no doubt be learned in this field in the 

 near future. 



i. The Mechanism of the Synthetic Reaction 



In bond-breaking and bond-forming respects the reaction which is illus- 

 trated below is similar to those discussed in earlier sections. 



OH 



I04a A. B. Pardee and I. Williams, Ann. inst. Pasteur, 84, No. 1, 147 (1953). 



