VIRUS-INDUCED ACQUISITION OF METABOLIC FUNCTION 31 



viral-induced types of thymidylate synthetase are indistinguishable by 

 this test. 



Other virus-induced enzyme and protein syntheses. In Figure 7 is 

 presented a summary of new and stimulated syntheses induced in 

 infection by a T-even phage. After the initial description of the appear- 

 ance of the three systems presented above, dCMP hydroxymethylase, 

 thymidylate synthetase, and dCMP deaminase, a number of other 

 laboratories undertook to study a cellular system in which the insertion 

 of a chemically unique viral DNA induced the rapid production in all 

 cells of many unique enzymes essential to the rapid multiplication of 

 the viral DNA and many other viral-specific proteins. Many questions 

 could still be posed concerning the exclusion of cytosine and the steps 

 involving purine nucleotides, DNA polymerase, glucosylation, etc., in 

 the synthesis of virus DNA. 



In testing to see whether the DNA polymerase of T2-infected cells 

 was specific for HMC nucleotides, it was observ^ed that infected cells 

 elaborated a specific dCTPase, which removed pyrophosphate from 

 dCTP to form dCMP ( Kornberg et al, 1959; Koerner et al, 1959; Som- 

 erville et al, 1959). Thus a compound essential for the formation of 

 bacterial DNA was eliminated, i.e., dCTP, providing the dCMP es- 

 sential for the formation of dHMP via the hydroxymethylase. The 

 dCTPase is not produced in T5 infection. 



According to Koerner (personal communication), the activity of 

 dCTPase in T2-infected cells is ten times as much as is necessary to 

 generate the dCMP as a substrate for hydroxymethylation. It may be 

 pointed out as well that this is also consistent with the possibility that 

 all deoxyribotides are derivable via cytosine nucleotides. 



Several laboratories (Somerville et al, 1959; Kornberg et al, 1959) 

 have also described the phosphorylation of dHMP and the production 

 of dHDP and dHTP. Although I have presented this as two new steps, 

 in this reaction and indeed in the activation of all the deoxyribonucleo- 

 tides to the triphosphate level, it is not certain that two separate 

 specific enzymes are involved. The dCMP kinase of Azotobacter vine- 

 landii forms only the diphosphate ( Maley and Ochoa, 1958 ) , and the 

 conversion of dCDP to dCTP can be effected by phosphoenol pyruvate 

 and pyruvic kinase. It would be of interest to know whether pyruvic 

 kinase fulfills this role in infected cells for other deoxynucleoside di- 

 phosphates. The dCMP kinase is not produced in E. coli after T2, T3, 

 and T7 infections; however, a marked increase in activity appears in 

 T5 infection ( Kornberg et al, 1959, Bessman, 1959 ) . 



Ten- to twenty-fold increased activities have also been observed 

 in T2, T4, T6, and T5 infection for dGMP kinase and dTMP kinase but 

 not for dAMP kinase. The last appears to be present in uninfected 

 cells in excess (Kornberg et al, 1959, Bessman, 1959). The increase in 



