CONTROL BY REPRESSION 51 



might, for example, largely be due to a requirement of the ^-galac- 

 tosidase-formiug maehinery for an in situ produetion of ri])onueleic 

 acid, under the direction of " deoxyribonucleic acid, to facilitate the 

 relati\ eh- rapid ribosome metabolism that would be necessary imder 

 conditions of induction (absence of repression). Even if so, the 

 possibility of repressor action at the primary-template level is by no 

 means excluded. 



The Secondary Template as a Possible Site of Repressor 

 Action. Strong arguments can be made in favor of repressor action 

 at the secondary-template level; in fact, the weight of the evidence 

 seems to lean heavily in this direction. Support for repressor action 

 at this level is provided, for example, by (a) the speed of onset of 

 repression; (b) the speed of onset of derepression or induction; (c) 

 the constant differential rates of /3-galactosidase induction in per- 

 mease-deficient organisms; (d) general protein synthesis in enucle- 

 ated organisms; (e) enzyme synthesis, including repressible enzyme 

 sxnthesis, apparently without concomitant ribonucleic acid forma- 

 tion; and (f ) the semiautonomous behavior of ribosomes. This sup- 

 port is particularly firm, if these pieces of evidence are taken in 

 conjunction with one another. For instance, the promptness of onset 

 of repression, taken bv itself, would seem to favor the secondary 

 template as repression site; this promptness would, however, not 

 eliminate the primary template from consideration, since repression, 

 at this level, could interfere with the production of a ribonucleic 

 acid species that might be continuously required for enzvme forma- 

 tion. Thus, repressor action, even at the primary-template level, 

 could express itself rapidly. However, in view of the fact that re- 

 pressible enzyme synthesis apparently can proceed without con- 

 comitant ribonucleic acid formation, the promptness of onset of 

 repression gains strength as evidence in favor of repressor action at 

 the secondary-template level. 



Accordingly, we are led to the view that enzyme repression and 

 induction probably can occur at the level of the ribonucleic acid 

 template, and hence of the ribosome. A possible mechanism of re- 

 pression ( and induction ) at the level of the enzyme-forming system 

 has been proposed in the regulator hypothesis in terms of the sepa- 

 ration of template products from their templates ( see the discussion 

 The Regulator Hypothesis). The available evidence is consistent 

 with such a picture, which can now be viewed in the context of ribo- 



