206 



ROBERT L. SINSHEIMER 



400 r 



S 200 



15 20 25 30 



Minutes 

 Fig. 3. Amounts of viral (HMC-containing) and bacterial (C-containing) DNA 

 per infected bacterium during growth of phage. (One DNA unit = 8.3 X 10 -14 mM 

 HMC for T2 DNA or 1.3 X 10~ 13 M M C for bacterial DNA.) [From A. D. Hershey, 

 J. Dixon, and M. Chase, J. Gen. Physiol. 36, 777 (1953).] 



was first explored by Hershey et al. 63 and has since been employed in the 

 study of phage DNA synthesis under a variety of experimental condi- 

 tions. 98 ' " 



Hershey's experiments indicated that in normal infection with T2 phage 

 an increase in acid-precipitable hydroxymethylcytosine-containing DNA 

 can first be observed at about 5 minutes after infection (Fig. 3). More 

 sensitive isotope dilution experiments by Vidaver and Kozloff 98 suggest that 

 little increase over the hydroxymethylcytosine brought in by the infecting 

 particles can be observed until about Q}i to 7 minutes. Following this 

 onset, phage DNA synthesis proceeds at an increasing rate until about 10 

 minutes at which time the rate reaches a maximum value of about 5 to 10 

 phage units per minute per cell 63 ' 98 ' 99a ' 10 ° (one phage unit of T2 DNA 

 equals 2 X 10" 11 M g- P 100 ). 101 



98 G. A. Vidaver and L. M. Kozloff, J. Biol. Chem. 225, 335 (1957). 



99 R. L. Nutter and R. L. Sinsheimer, Virology 7, 276 (1959). 



99a S. S. Cohen, Cold Spring Harbor Symposia Quant. Biol. 12, 35 (1947). 



100 A. D. Hershey and N. E. Melechen, Virology 3, 207 (1957). 



101 The maximum rate of phage DNA synthesis is dependent upon the nature of the 

 nutrient medium, being greater in a broth medium than in a synthetic medium. 

 In the latter — glucose-ammonium — the rate of DNA synthesis in the culture in- 

 creases more than tenfold after infection and is nearly double the combined rate 

 of DNA and RNA synthesis in the uninfected bacterium. 98 - 10 ° In broth-grown 



