116 CONTROL MECHANISMS IN CELLULAR PROCESSES 



This activation may lead only later to an increase of specific RNA 

 synthesis, thus assuring continuous enhanced function of enzyme- 

 forming sites. 



If the first assumption is correct, the inducer should act directly 

 on RNA production, i.e., it should activate the gene. As a result, 

 new RNA molecules would be formed and transferred to the cyto- 

 plasm. There, enzyme production would start and the production 

 rate would be proportional to the number of RNA molecules present. 

 As long as the gene acts and there is no destruction of RNA, the 

 rate should steadily increase. The rate of formation of induced 

 enzymes is rather constant for a period of time ( Pollock, 1959 ) . This 

 implies either that all the necessary RNA molecules are produced 

 right at the beginning of the induction, or that the new RNA mole- 

 cules are soon inactivated so that a steady state is quickly reached. 

 The first could explain the case of penicillase production. In the 

 initial 10 minutes of the lag period, the enzyme production rises to 

 a constant rate and remains there for a long time. The ability to 

 produce penicillase is retained by the cell long after the inducer is 

 removed ( Pollock, 1959 ) . If the removal of the inducer puts a halt 

 to RNA synthesis, the continued synthesis of the enzyme could be 

 explained only by a long half -life of existing RNA-enzyme-forming 

 sites. This explanation is at variance with Pollock's explanation, 

 which is that molecules of the inducer combine somehow with the 

 activated site and keep it active for an extended period. 



The case of /3-galactosidase would follow the second scheme. 

 Newly formed RNA is soon destroyed. As soon as the inducer is 

 removed, enzyme-forming sites are inactivated and further enzyme 

 formation stops. The picture is complicated slightly by the fact that 

 the enzyme, once formed, remains active in the cell for a long time 

 (Wainwright and Pollock, 1949; Rickenberg et ah, 1953). 



The opposite of induction and an active field of research today 

 is enzyme repression. In the case of repression, an enzyme is pro- 

 duced until a product of enzyme action, be it immediate or remote, 

 accumulates to stop its production. In a preceding paper, Vogel 

 ( 1961 ) gave us all the facts known of the phenomenon and discussed 

 a possible explanation of its mechanism. I would like briefly to con- 

 sider repression within the framework of our hypothesis of gene 

 action. If we consider a gene as intrinsically active, the presence of 

 a repressor would stop its activity, through a mechanism not unlike 

 that of induction. In some cases the repressor may compete with 



