114 CONTROL MECHANISMS IN CELLULAR PROCESSES 



mosome (and the specific gene) or should diffuse freely through the 

 cell so that it would be highly probable that it would enter into 

 contact with the gene site. Small molecular products of cell metab- 

 olism would be the probable signal carriers. The cell then could 

 inform the gene about the functional state of RNA and the enzyme 

 it produces by sending back either products or substrates of enzyme 

 action. 



In many cases gene activity should not depend on one particular 

 enzymatic reaction, but rather on a state of more complex metabolic 

 processes. An effective control in this case may demand simultane- 

 ous occurrence of several signals or of substances which are not 

 exactly related to the enzymatic reaction controlled by the gene. 

 Some possibilities of this kind will be discussed later. 



After presenting the theoretical considerations for an hypothesis 

 of gene activation, I would like to inquire whether there are facts 

 to support it. First: Is it a fact that RNA is formed unequally in 

 different phases of cell life and does RNA formation precede the 

 formation of new proteins, when they appear in the cell? Second: 

 What are the possible factors involved in gene activation? 



Enzyme Induction and Repression. One of the best studied cases 

 where a cell starts to produce a new protein is that of inducible 

 enzymes. There is an excellent recent review on this subject (Pol- 

 lock, 1959) and in the present volume, Vogel considers the prob- 

 lem of enzyme induction and repression. I shall try only to see how 

 the established facts support the proposed hypothesis of gene action 

 and RNA function. 



The distinction between constitutive and inducible enzymes is 

 not absolute, inducible enzymes being formed in the absence of the 

 inducer in very small quantities. The cell, therefore, contains a 

 gene which determines the amino acid sequence of the enzyme. 

 The quantity of the enzyme produced is governed by the presence 

 or absence of an inducer. Where does the inducer act? It has been 

 well established that induction initiates enzyme formation from free 

 amino acids. This gives us two possible sites of activation: either 

 the RNA molecule, which is the enzyme forming site, or the gene, 

 the specific RNA forming site. 



If the induction occurs at the level of the RNA molecule, this 

 would imply that such molecules are continuously present in the 

 cell. Induction then should be possible in the absence of RNA 



