THE ACTION OF IONIZING RADIATION ON THE 

 CELLULAR SYNTHESIS OF PROTEINj 



ERNEST POLLARDJ 



Biophysics Department, Yale University, Neiv Haven, Connecticut, U.S.A. 



SUMMARY 



The experiments described are all in accord with the idea that the immediate 

 synthesis of protein is caused by organelles which are sensitive to ionizing radi- 

 ation in the manner expected for ribosomes in an extended form. The volume of 

 the sensitive regions agrees with the volume of an SOS ribosome and this, inde- 

 pendently, substantiates the work of McQviillen, Roberts and Britten (1959) 

 who have shown that the short term incorporation of ^^S04 is into 70S ribosomes. 



The long term effects of radiation are much more difficult to interpret. In 

 separate experiments we have found that there is a reduction in the rate of in- 

 crease of DNA in irradiated cells. Possibly this means that there is some kind of 

 disruption of the bacterial nucleus which produces an unbalance in the cell and 

 reduces cellular synthetic action later on. Partially successful attempts to express 

 this theoretically have been made (Pollard, 1960), but it cannot be claimed that 

 the process is fully understood. 



Synthesis of protein is an essential characteristic of every Hving 

 system. It is now known that it takes place in several stages and that 

 different mechanisms are involved with each. The present studies were 

 made with the aim of using the disruptive action of ionizing radiation 

 to give some information on the nature of the process of protein syn- 

 thesis. The work reported is not complete: it is still in i^rogress. Never- 

 theless some definite facts have been established and some conclusions 

 can be drawn regarding protein synthesis, and also on the sensitivity of 

 some parts of the cell to ionizing radiation. 



The cell employed throughout the work is the bacterium EschericJiia 

 coli. 



PHYSICAL ACTION OF IONIZING RADIATION 

 The pioneer work of Lea and others in the pre-war years has been 

 greatly extended in the past ten years in the Yale Biophysics Depart- 

 ment. The work has been reiiorted in various review articles (Pollard, 



t The work reported here was largely supported by the U.S. Atomic Energj' Com- 

 mission. 



J For 1960-Gl visiting Professor at the Pemisylvania State University. 



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