CHEMISTRY AND VIRAL GROWTH 



cussed here. For T2 none of the biological tests of this idea are 

 applicable, but chemical tests are. 



As already mentioned, the first cytochemical effect of the 

 infection is a rapid dispersal of the bacterial chromatin (44). 

 By chemical analysis, one observes a more or less complete dis- 

 appearance of cytosine-containing DNA, and the atoms of this 

 DNA are rapidly incorporated into viral DNA. The conver- 

 sion appears to be highly efficient. The direct analytical re- 

 sults indicate a phosphorus transfer of 50 per cent (22,54), sub- 

 ject to the assumption that all the transferred phosphorus comes 

 from bacterial DNA. This becomes nearly 100 per cent when 

 corrected for the fact that only half the phosphorus of the bac- 

 terial DNA fraction, but nearly all the phosphorus in isolated 

 phage, is really DNA phosphorus (28). Similar conclusions 

 follow when the transfer of C^ ^-labeled bacterial precursors is 

 measured. All the DNA purine and pyrimidine carbon (ex- 

 cept cytosine), and all or most of the carbon of specifically 

 labeled bacterial DNA-thymine, appears either in viral DNA or 

 in residual bacterial DNA in infected bacteria (29). The con- 

 version is more or less complete, and occupies the first 30 minutes 

 of viral growth. 



One would like to interpret these facts as an illustration of 

 Luria's idea of parasitism at the genetic level. Before doing so, 

 two questions have to be answered. First, does the virus cause 

 the breakdown of bacterial DNA, or merely block its resyn- 

 thesis? Second, is bacterial DNA the only characteristic bac- 

 terial substance that is used to make virus? 



The first question has been answered by showing that 

 bacterial DNA, and indeed characteristic bacterial substances in 

 general, do not turn over at rates comparable to rates of syn- 

 thesis in growing bacteria (25). Moreover, bacterial RNA does 

 not turn over appreciably in infected bacteria (8,22,48). State- 

 ments made about turnover are, of course, intelligible only in 

 terms of actual experiments. Two examples will suffice here. 

 The presence of thymidine in unlabeled culture micdium during 

 viral growth will specifically suppress the conversion of labeled 



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