782 BIOCHEMISTRY: KORNBERG ET AL. Proc. N. A. S. 



Kinetics of Enzyme Development and Enzyme Reactions. — The temporal pattern 

 of development of all the enzymes studied in this report that were either "new," 

 or the levels of which were significantly raised, was similar. The first traces of 

 change were apparent at four minutes after T2 infection and about ten minutes after 

 T5 infection. While the precision of measurement of these time intervals is not 

 great, it is clear that there is a time lag before significant levels of these enzyme 

 activities appear. Several groups of investigators^^' "• ^^ have shown that 5- 

 methyltryptophan and chloramphenicol administered to cells at levels sufficient 

 to inhibit protein synthesis also blocked DNA synthesis when given before or up 

 to about 5 min after infection. When given 10 min or later following T2 infection, 

 the inhibition of protein synthesis had only a small or even no effect on the rate of 

 DNA synthesis. It seems reasonable to consider that the time lag we have ob- 

 served may be related to the chloramphenicol-sensitive interval required for 

 development of the enzymatic machinery for DNA synthesis, as well as other 

 protein components vital to virus information. There have been indications of 

 non-phage protein synthesis immediately upon infection ^^ and it remains to be 

 determined what fraction of this protein can be identified with the enzymes de- 

 scribed here. 



The multiplicity of enzyme changes described in this study along with the 

 findings on the hydroxymethylating^ and deo.xyuridylate-methylating^" enzymes, 

 are all directly related to DNA synthesis. Enzyme measurements related to 

 other metabolic pathways in infected cells have as yet disclosed few significant 

 changes." It would be surprising if further exploration of the phage-infected 

 cell failed to reveal additional examples of new or augmented enzyme activities 

 related to the requirements imposed by rapid phage synthesis. 



In view of the pitfalls inherent in assaying the level of an enzyme activity in a 

 cell extract, let alone in the cell iteelf, a detailed evaluation of the various enzyme 

 values in terms of virus DNA synthesis does not seem warranted. However, it 

 is interesting to note that the rates of the kinases and the glucosylating enzyme 

 are all greater than that found for the DNA polymerizing activity and, further, 

 that the increase in the latter activity over levels found in uninfected cell extracts 

 is about the same as the increase in DNA synthesis in whole cells following T2 

 infection. Also it is remarkable that the dA-5-P kinase activity (very likely 

 identical to adenylate kinase) is about 10 times that of the other deoxynucleotide 

 kinases in the uninfected cell extract and does not change upon T2 infection, 

 while after infection the other kinases and hydroxy methylase reach levels com- 

 parable to the dA-5-P kinase. Finally, it is noteworthy that the dC-5-P kinase 

 activity does not increase upon T2 infection but remains at the relatively low 

 level observed in the uninfected cell, whereas it increases about 10-fold upon T5 

 infection. 



References to increases in level of a preexisting enzyme carry no implication 

 that the additional enzyme activity is identical to the old or even that more 

 enzyme has been synthesized "de novo." To resolve this important point, it will 

 be necessary to characterize isolated preparations of the normal- and infected- 

 cell enzymes and to establish by tracer techniques that the enzymes developed after 

 infection have, like induced enzymes,^- been synthesized from the amino acid pool. 



Control of DNA Synthesis by the Nature of the DNA Primer. — Perhaps the most 



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