VERUS-INDUCED ACQUISITION OF METABOLIC FUNCTION 



21 



monoglucosyl HMC; while T2 contains mainly monoglucosylatcd and 

 non-glucosylated I IMC. HMC has thereby been implicated in mecha- 

 nisms of parasitism and virulence, survival, and speciation among the 

 T-even viruses. 



The biosynthesis of thymine and hydroxymethyl cytosine. In ex- 

 ploring the biosynthesis of viral pyrimidine, it was found that exog- 

 enous orotic acid and pyrimidine of host DNA could be converted to 

 viral HMC and thym.ine. The -CHoOH and -CH3 of the latter bases 

 were derived from the ji-coxhon of serine (Cohen and Weed, 1954). 

 The methyl group of thymine did not come from the methyl of methio- 

 nine (Green and Cohen, 1957). A series of nutritional experiments 

 with bacterial mutants and competition experiments with infected 

 cells then revealed that the addition of the one-carbon fragments to 

 form viral bases did not occur at the level of free bases or nucleoside. 

 In order to test the syntheses at the nucleotide level it was necessary to 

 study these possible reactions in cell-free extracts. 



Friedkin and Kornberg (1957) demonstrated the presence of an 

 enzyme, thymidylate synthetase, in extracts of normal E. coli which 

 produced thymidylate (dTMP) f rom , deoxyuridylate (dUMP), for- 

 maldehyde, and tetrahydrofohc acid (THFA), as presented in Figure 

 2. Testing for similar reactions with deoxycytidylate (dCMP) in nor- 

 mal and T2-infected E. coli, it was possible to show that with dCMP 



OH 



^ N 



+ HCHO + 2H Itif^ 



N 



OH 



A^CH: 



0-n" 



+ H2O 



DR-5'-P 

 DEOXY - U M P 



DR-5'-P 



THYMIDYLIC ACID 



THFA 



+ HCHO 



DR-5-P 

 DEOXY -CMP 



O 



NH2 

 ,s^\p CH^H 



/ 

 N 



DR-5'-P 



5-HYDROXYMETHYL- 

 DEOXY-CMP 



Figure 2. The utilization of formaldehyde in the enzymatic synthesis of diy- 

 midylate and 5-hydroxymethyl deoxycytidylate. 



