no CONTROL MECHANISMS IN CELLULAR PROCESSES 



of different proteins and arranging amino acids in as many different 

 sequences. It should be expected that such a buildup would pro- 

 ceed stepwise, via small peptides, and then many proteins should 

 have these peptides in common. There is, however, no evidence to 

 support this view while the evidence of protein synthesis from free 

 amino acids is ample. 



More pertinent facts and arguments on the role of RNA in protein 

 synthesis may be found in recent reviews written on this subject 

 (Marshak, 1958; Roberts et al, 1959; Cohen and Gros, 1960). In 

 conclusion, all the facts support the generally accepted hypothesis 

 DNA —* RNA —> protein. In the next two sections I would like to 

 discuss how, in the light of this hypothesis, RNA could control cellu- 

 lar processes. 



Control of RNA Production 



Genie Control. Cellular processes must be somehow controlled 

 by genes, since the nature of a cell or organism depends on its gen- 

 etic constitution. Genetic control can be exerted either directly, 

 through the quality and the rate of production of primary gene 

 products, or indirectly, at different levels, through an intricate in- 

 terplay of biochemical reactions ( Strauss, 1955 ) , directed by primary 

 or secondary gene products. If we think of enzymes as products 

 of gene action, then genes should determine the nature of these 

 enzymes, the rate of their formation, and the time when they are 

 formed in the cell life. Enzymes, once in the cytoplasm, direct in- 

 numerable biochemical reactions, and their mutual action results 

 in orderly functioning of cell metal:)olism. The rates of enzymatic 

 processes are subject to many factors (Pardee, 1959), such as the 

 supply of precursors, the quantity of enzyme present and the func- 

 tional state of enzymes, determined by their properties and environ- 

 mental conditions. 



The gene determines the specificity of a protein molecule by im- 

 posing a certain order of amino acids in the polypeptide chain. 

 This it does by the intermediary of an RNA particle. The problem 

 of the genie control of enzyme structure has been discussed else- 

 where in this symposium (Suskind and Yanofsky, 1961) and in a 

 recent book (Anfinsen, 1959). The quantitv of an enzyme present 

 in the cell and also the relative quantity of different proteins ( some 

 may be without enzymatic function), characteristic of every cell, 



