264 LOCALIZATION OF RADIATION EFFECTS 



activities greater than 50 curies per gram are required. Such samples 

 can be prepared using the present uranium-pile installation, apparently 

 without marked changes in routine procedures. However, the po- 

 tentialities of these researches warrant increasing efforts to produce 

 large amounts of the various radioactive isotopes needed with specific 

 activities some orders of magnitude greater than are now available 

 routinely. 



REFERENCE 



1. Taylor, J. F., S. F. Velick, G. T. Cori, C. F. Cori, and M. W. Stein, J. Biol. 

 Chem.,' 173:619, 1948. 



DISCUSSION 

 Rubin: 



Absorbed P^^ was found to increase significantly the rate of mutation at a 

 specific locus in E. coli (streptomycin resistance). 



The calculation of the distribution of P^^ decays of such low energy as to in- 

 crease significantly the specific ionization in the cells shows no great difference 

 from Kamen's calculations. 



Wyss: 



The decay of radioactive P to S might be of primary importance. The phage 

 containing such a substitute for P might readily invade a bacterial cell but could 

 not there reproduce itself because of the absence of identical building blocks, 

 that is, nucleic acids containing S instead of P. In Kamen's experiments such 

 a phage is recorded as being non-infective, and the impUcation is that it became 

 non-infective during the emanation. 



Kamen : 



It is not obvious that a single sulfate radical-containing nucleotide would 

 necessarily be unavailable for synthesis into a nucleic acid. Such a "thionu- 

 cleotide" would be only a slight modification of the natural nucleotide and might 

 be used to synthesize a slightly modified macromolecule in which only 1 in several 

 100,000 P atoms was replaced by an S atom. When it is possible to prepare 

 sulfur analogs of nucleotides, it will be interesting to see how well the nucleic 

 acid synthesis system is able to incorporate them into the natural nucleoprotein. 



Failla : 



It could also be assumed that only the low-energy beta particles produce 

 enough ionization in the phage; that is to say, only the low-energy beta particles 

 will have a high probability of effectiveness and of consequent biologic change. 



Powers: 



The experiments at Argonne on the phenomenon reported today have given 

 qualitatively the same result.* In Paramecium aurelia it has been shown that 



* Powers, E. L., Genetics, 33: 120, 1948. 



