PROTEIN SYNTHESIS 113 



The Systems Concerned in Protein Synthesis 



At the date of writing the main contribution, from the cyto- 

 chemical point of view, to our knowledge of the systems con- 

 cerned in protein synthesis has come from the laboratory of 

 T. Caspersson in Stockholm. These contributions have been 

 published in a series of papers commencing in 1932, and have 

 been summarised in a recent monograph entitled Cell Growth 

 and Cell Function (1950) . Probably the most important of these 

 contributions has been the observation of the constant associa- 

 tion of nucleic acids with protein formation. In his monograph 

 Caspersson recapitulates the generalization made by Caspersson 

 and Schultz, based on the study of nuclei, bacteria, viruses, etc., 

 "that all self-reproducing protein molecules need the coopera- 

 tion of nucleic acids for reproduction" (p. 100). Caspersson 

 also states that "the nucleic acids take part in the processes 

 leading to the synthesis of cellular proteins, not only in the 

 nucleus but also in the cytoplasm" (p. 140) . These views have 

 illumined many previous observations and have inspired a re- 

 markable volume of work by other investigators in a wide variety 

 of fields. 



In pursuing the further analysis of the association of protein 

 synthesis and nucleic acids, there are three important questions 

 which will be considered here. These are: . 



1. Do nucleic acids participate chemically in protein synthesis? Alter- 

 natively, 



2. Are nucleic acids essential chemical or physical components of the 

 environment in which protein synthesis occurs? 



3. What are the sites of protein synthesis? 



To obtain a satisfactory answer to question 1 is by no means 

 simple. For example, if the nucleic acids had catalytic functions, 

 it is unlikely that chemical changes in the nucleic acid during 

 protein synthesis could be detected even by the use of isotopes. 

 On the other hand, if the phosphate groups of nucleic acids par- 

 ticipated in protein synthesis, it is likely that a phosphorus turn- 

 over could be detected by isotopic studies. 



Question 2 is also by no means simple, for there are many con- 

 ceivable functions of nucleic acids which fall within the frame- 



