RADIATION AND THE CELLULAR SYNTHESIS OF PROTEIN 87 



cell debris, the pellet formed after three hours' centrlfngation at 1 20,000 g 

 was taken to be ril)osomes, following the work of Roberts et al. (1958). 

 The amount of 32p and ^sg in the ribosomes of irradiated cells was com- 

 pared to that in normal cells, in both cases after incubation for 60 min 

 with labelled PO4 and SO4. The results obtained, in work in collabor- 

 ation with R. Wax, are shown in Fig. 8. In the case of 32p there seems 

 to be a very slight increase in the incorporation of 32p into the ribo- 

 somes for small doses. For higher doses the proportion falls, with a 

 sensitivity which corresponds to that found for the uptake of amino 

 acids. In the case of ^^S there is a fall to a constant level. 



REFERENCES 



Hutchinson, F. (1960). A7ner. Nat. 94, 59. 



McCrea, J. F. (1960). Ann. N.Y. Acad. Set. 83, 692. 



McQuiLLEN, K., Roberts, R. B., and Britten, R. J. (1959). Proc. nat. Acad. Sci., 



Wash. 45, 1437. 

 Pollard, E. C. (1959). Rev. 7nod. Phys. 31, 273. 

 Pollard, E. C. (1960). Amer. Nat. 94, 71. 

 Pollard, E. C, and Barrett, N. (1959). Radn Res. 11, 781. 

 Pollard, E. C, Guild, W. R., Hutchinson, F., and Setlow, R. B. (1955). Progr. 



Bio])hys. biophys. Chem. 5, 72. 

 Roberts, R. B., Britten, R. J., and Bolton, E. T. (1958). In "Microsomal Particles 



and Protein S^Tithesis", pp. 84-94. (R. B. Roberts, ed.) Washington Academy of 



Science. 

 Roberts, R. B., Cowie, T>. B., Abelson, P. H., Bolton, E. T., and Britten, R. J. 



(1957). Carnegie Institution of Washington, Publication 607, Washington D.C. 



DISCUSSION 



HERCiK : Is there really a bend in the first curve? 



POLLARD : It is possible that it may depend on the precision of measurements and 

 at jjresent we should be cautious about it. We have as yet but few data pointing 

 to the presence of a bend. 



MARCOViCH : Is there a formation of the inductive enzyme within the cell or does 

 an inhibition of the enzymatic activity take place? 



POLLARD : This is not yet clear. It would be interesting to find such an inducing 

 agent which would not itself be a metabolite. 



ALEXANDER: While calculating the sizes of the protein particles in complex 

 systems did you take into consideration the possibility of energy transfer from 

 one molecule to another? 



POLLARD : Experiments carried out on jDure substances and on non-purified pre- 

 parations (for example on pure DNA and on DNA in yeast) have shown that the 

 accompanying substances do not alter the effect considerably, only about two- 

 fold. 



ALEXANDER : Protection by transfer of energy to other substances may alter the 

 effect not twofold, but up to tenfold. 



