INDUCED ENZYME FORMATION 



sudden stimulation of protein synthesis caused by the amino 

 acid addition would exert an exhaustive demand on the meta- 

 bolic devices which supply the derivatives needed for ribonu- 

 cleic acid synthesis. In view of the suggested sensitivity of the 

 beta-galactosidase-forming system to the supply level of the 

 RNA precursors, the addition of amino acids might be expected 

 to result in an inhibition of beta-galactosidase formation. This 

 prediction is experimentally realized (30). Thus, the presence 

 of inducer fails to stimulate enzyme formation if amino acids are 

 added simultaneously. The suppression is virtually complete 

 for a period of a half hour, following which some recovery of 

 enzyme-forming capacity occurs. That the inhibition is re- 

 lated to RNA precursor supply is supported by the ability of 

 purine and pyrimidine bases to reverse it. 



This dependence of enzyme formation on an adequate 

 supply of nucleic acid precursors has also been exhibited (7) in 

 the case of alpha-glucosidase formation in S. cerevisiae In ad- 

 diton to their free amino acid pool, yeasts also possess a consi- 

 derable internal supply of nucleotides and their polyphosphate 

 derivatives (68). It was found possible (7) to specifically de- 

 plete the nucleotide pool by incubation in the presence of an ex- 

 ternal supply of amino acids and energy. This treatment leads 

 to a loss of enzyme-forming capacity while leaving the free amino 

 acid pool intact. If cells are first partially induced and their 

 nucleotide pool then depleted, they fail to form enzyme on being 

 again exposed to inducer. If their nucleotide pool is, however, 

 replenished, enzyme synthesis proceeds normally. These ex- 

 periments illustrate in a different manner and with another sys- 

 tem the apparent requirement that RNA synthesis be possible if 

 enzyme formation is to continue. 



EXPERIMENTS WITH SUBCELLULAR FRACTIONS 



The experiments thus far described strongly implicate RNA 

 as the template in the process of enzyme synthesis. They cannot, 

 however, be taken as conclusive. It is painfully obvious that 

 although interesting and perhaps even ingenious experiments can 



153 



