ivfi H. H. ItoHKHTS, H. .1. HHITTEN, AND D. J. MCCAHTHV 



rrutilization ivciuiri's tlu' inti'oductioii of the cuiicci)t of a "i)ri\'atc' pool," 

 i.e.. a pool of nucleic acid prt'cuisoi> t^cparate from the usually observed 

 pool of TCA !>olul)]c material. Such a "private pool" could in itself be the 

 cause of the appaicnl change in comi)osition. If exogenous P'-O^ had 

 a pathway giving direct entiy into D-RNA while entry into S-RNA and 

 R-RNA was delayed by a precursor pool, the newly formed RNA would 

 show the composition of D-RNA. 



As a third alternative D-RNA could be converted in part to R-RNA 

 by the addition of purines without extensive degradation. Such a process 

 would also result in a change with time of the apparent composition. 



At pi'esent, no certain choice can be made among these and other 

 possible alternatives. None are completely satisfying and none are com- 

 pletely excluded by the experimental data. The only certainty is that the 

 reactions are complex and elusive. 



IX. Discussion 



A. ROLE OF RIBOSOMES IN INFORMATION TRANSFER 



The preceding sections have presented facts concerning the ril)Osoraes, 

 and tlie flow of material through three stages of ribosome synthesis. 

 These facts provide no direct indications of the part ribosomes may play 

 in directing the formation of i)rotein in accord with the information 

 carried by DNA. However, they provide necessary conditions which 

 must be met by any theory of intermediate processes in information 

 transfer. 



At the present time it is easier to provide a reasonable interpretation 

 of a complicated set of biological facts than to demonstrate that one 

 particular interpretation does in fact correspond to nature. For example, 

 it is currently accepted that ribosomes provide the active sites and tem- 

 plates for protein synthesis. The basis for this belief is (1) that the rate 

 of protein synthesis is proportional to the ril)Osome content, (3) that 

 ribosomes are essential for protein synthesis in cell free systems, and 

 (3) that newly formed protein is associated with ribosomes. 



However, one who had reason to believe that ribosomes were not the 

 protein synthesizing sites might interpret the same facts as follows. (1) 

 That a high rate of protein synthesis is required for the formation and 

 accumulation of ribosomes, (S) that an enzyme required for protein syn- 

 thesis is firmly bound to ribosomes, and (5) that newly formed protein 

 is readily adsorbed by ribosomes. 



The correlation of facts relating to the flow of material with another 

 set of facts relating to the flow of information is extremely difficult. In 

 most experiments only the average flow of material into all proteins 



