450 



( HAM I.R 35 



dHMCP 

 i 



CPP _J\ 



dCP 



k 



dTP 

 i 



upp _JTl 



i 



dUP^_ 



dHMCP kinase 



deoxyribosidase 



dHMCPP kinase 



dHMCPPP 



ATP 



dCPP 

 3 . 



dAPP 



ATP 

 deoxyribosidase 



ATP 



dUPP kinase 



_»» dUPPP 



ATP 

 dUPPPase 



glucosyl 

 transferases 



t 



glucosyl 



DNA 



figure 35-1. Enzymatic pathways leading to DNA synthesis in E. coli. Interrupted 

 arrows denote reactions occurring and wavy line to reaction blocked in cells infected 

 with T-even phages. {After M. J. Bessman, 1963.) 



Such T-requiring E. coli can, however, syn- 

 thesize thymidylic acid — thymidylate — when 

 infected with c/>T2 because, as was proven, 

 T2 carries the information to make a chro- 

 matographically different but similar-acting 

 thymidylate synthetase. ) The c/UP involved 

 has at least two sources. One source, 

 cVUPPP, loses pyrophosphate through the 

 action of dUPPPase; another, c/UPP, loses 

 one phosphate (orthophosphate) and be- 

 comes i/UP. The deoxyriboside 5'-mono- 

 phosphates of C, A, G, and T are phos- 

 phorylated to the 5'-diphosphate condition 

 by specific phosphorylating enzymes — nu- 

 cleoside monophosphate kinases — in the fol- 

 lowing reaction: 



i-yp . AT-p nucleoside monophosphate kinase 



c/XPP + ADP ("adenosine 5'-diphosphate) 



where X is the nucleoside of C, A, G, or T. 

 (It should be noted that the dGP, c7TP, and 

 <7CP kinases formed in E. coli infected with 

 virulent phage are different from those 

 produced in uninfected cells.) The deoxy- 

 riboside 5'-diphosphates produced are most 

 probably converted to the 5'-triphosphate 

 condition by means of other specific phos- 

 phorylating enzymes — nucleoside diphos- 

 phate kinases. The reaction is as follows: 



<7XPP + ATP 

 iVXPPP + ADP. 



nucleoside diphosphate kinase 



