212 ROBERT L. SINSHEIMER 



from the host DNA and host intermediates, possibly some from RNA, and 

 largely from inorganic phosphorus assimilated after infection. Pulse P 32 ex- 

 periments have shown that, on the average, the transport of a P 32 atom from 

 medium to phage DNA requires about 8 to 9 minutes. A DNA molecule 

 remains in the phage precursor pool an average of an additional 7 to 8 

 minutes. 100 ' 103 



Studies of the acid-soluble fraction of infected cells 114 have demonstrated 

 the presence of compounds related to DNA precursors such as deoxyadeno- 

 sine triphosphate (dATP), deoxyguanosine monophosphate (dGMP), de- 

 oxyuridine monophosphate (dUMP), and thymidine diphosphate (TDP), 

 none of which were present in detectable amounts in uninfected cells. 

 Curiously, no nucleotide containing 5-hydroxymethylcytosine could be 

 found in the acid-soluble fraction. 



The contribution of parental DNA to progeny cannot be reduced by 

 addition of external guanine, adenine, or thymine, 104 which suggests that 

 this transfer does not involve degradation to a pool of small intermediates. 

 The contribution of thymine to progeny DNA from host DNA can, how- 

 ever, be reduced to a moderate extent by supplying the cell with thymidine 

 after infection. 104 



Lanning and Cohen 115 have shown that the formation of deoxyribose in 

 T6-infected cells appears to involve either a new pathway or a change in 

 the relative use of existing pathways. When glucose-1-C 14 is used as the 

 sole carbon source during infection, the deoxyribose of the phage DNA 

 has a specific activity 40-60% of that of the glucose of the medium. In 

 the same medium the deoxyribose of the DNA of normal bacteria has only 

 20-30 % of the specific activity of the glucose. 



Loeb and Cohen, 116 again using glucose-1-C 14 as the carbon source during 

 infection, demonstrated that the deoxyribose of all the nucleotides of the 

 T6 produced, had the same specific activity, indicating a common path of 

 formation for all the deoxyribose. These authors suggest that the precursors 

 of the viral deoxyribose are the acid-soluble ribonucleotides. 



The glucose coupled to the HMC of the T6 DNA appears to be derived 

 directly from the glucose of the medium 116 through uridine diphosphate 

 glucose. 77 



b. Enzymes Produced during Infection 



The development of several new enzymes during the first minutes of 

 infection with the T-even phages has recently been demonstrated. Flaks 

 and Cohen 117 " 119 have demonstrated an enzyme which in the presence of 



114 J. F. O'Donnell, R. P. Mackal, and E. A. Evans, Jr., J. Biol. Chem. 233, 1523 (1958). 



115 M. C. Lanning and S. S. Cohen, J. Biol. Chem. 216, 413 (1955). 



116 M. R. Loeb and S. S. Cohen, /. Biol. Chem. 234, 364 (1959). 



117 J. G. Flaks and S. S. Cohen, Biochim. el Biophys. Acta 25, 667 (1957). 



