ENZYMIC FORMATION OF DEOXYRIBONUCLEIC ACID III 



Our results were obtained with soluble enzymes and it remains to be 

 shown whether thev have any bearing on the problem of DXA synthesis in 

 living cells. It is not vet possible to decide this point with any degree of 

 certainty, but it seems to be relevant that recent experiments by Klenow 

 [lo] and by Morris and Fischer [ii] have shown that effects similar to 

 those I have discussed here can be obtained with living cells. It is thus not 

 inconceivable that such effects are parts of an important homeostatic 

 mechanism for DNA synthesis. 



References 



1. Romberg, A., in "The Chemical Basis of Heredity", ed. W. D. McElroy and 

 B. Glass, Johns Hopkins Press, Baltimore, 579 (i957)- 



2. Hammarsten, E., Reichard, P., and Saluste, E.,_7. biol. Chem. 183, 105 (1950). 



3. Rose, I. A., and Schweigert, B. S.,J. biol. Chem. 202, 635 (1953). 



4. Reichard, P., and Rutberg, L., Biochim. biophys. Acta 37, 554 (i959)- 



5. Reichard, P., Biochim. biophys. Acta 41, 368 (i960). 



6. Pardee, A. B., in "The Enzymes I", ed. P. D. Boyer, H. Lardy, and K. 

 Myrback. Academic Press Inc., New York, 681 (1959). 



7. Bollum, F. ].,jf. Amer. chem. Soc. 80, 1766 (1958). 



8. Mantsavinos, R., and Canellakis, E. S., j. biol. Chem. 234, 628 (1959). 



9. .\dler, J., Lehman, L R., Bessman, 'SI. J., Simms, E. S., and Romberg, A., 

 Proc. nat. Acad. Sci., Wash. 44, 641 (1958). 



10. RIenow, H., Biochim. biophys. Acta 35, 412 (1959). 



11. Morris, N. R., and Fischer, G. A., Biochim. biophys. Acta 42, 183 (i960). 



Discussion 



Chargaff : I was wondering whether Dr. Reichard has any explanation of the 

 peculiar fact that usually analogues are incorporated only into one of the two types 

 of nucleic acid. For instance, fluorouracil when given to E. coli will appear only as 

 ribofluorouridylic acid in RXA and not a trace seems to go as the deoxy compound 

 into DNA; similarly in the plant nucleic acids which I have mentioned in my talk 

 high amounts of 5-methylcytosine are found in the DNA only. I was wondering 

 whether you had any explanation for this. 



Reichard : In the case of uracil — and I think this also applies to fluorouracil, 

 because from all the work which has been published now it appears that fluorouracil 

 behaves with enzymes as does uracil — the explanation put forward by Romberg 

 is that there are no kinases for deoxy-UMP; this would also be true for fluoro- 

 deoxy-UMP. This is a reasonable explanation, but on the other hand I am a little 

 worried about the fact that our own findings indicate that the reduction might take 

 place at the diphosphate level. I don't know whether it is really LTDP which is 

 reduced to deoxy-UDP although I believe so. What one might look for would be a 

 special phosphatase like the one which has been found in T2 infected E. coli 

 for deoxy-CTP, but in this case it would be specific for deoxy-UTP. That could be 

 an explanation. 



Davidson : Is there evidence that the reduction step takes place at the diphos- 

 phate level in other cases than deoxy-CDP ? 



