352 Discussion 



time without having an inducer present; but it cannot make p-galac- 

 tosidase because it is altered in its galactosidase gene. The male is 

 inducible. 



What happens when the gene which has the ability to make p-galacto- 

 sidase gets into the cytoplasm which is constitutive? Do you find 

 enzyme formation or not? As soon as this gene enters the cytoplasm it 

 starts to make enzyme at full speed, within one or two minutes. This 

 result argues against any very elaborate synthesis of a lot of templates. 

 Consider the constitutive cytoplasm : the result means that the cyto- 

 plasm is ready to permit the formation of enzyme by this gene. There 

 are two possible explanations. One is that the cytoplasm is loaded with 

 inducers which are made inside the cell, so that as soon as the gene 

 enters, the inducers start acting. The other explanation is that the 

 cytoplasm is empty: there is a repressor in inducible bacteria which 

 prevents enzyme synthesis, but in constitutive bacteria the repressor is 

 missing so that when the gene escapes from the repressor it starts 

 making the enzyme. It seems that the repressor idea is the right one, 

 because when you inject the galactosidase-positive gene you also 

 introduce the inducible gene at the same time, and in about 30 minutes 

 after this gets in, conditions are changed so that the cell is no longer 

 constitutive, but has become inducible. You have to add an inducer 

 now to get the bacterium to continue making enzyme. Material has 

 been injected, from male to female, which creates something new that 

 limits enzyme formation. Both kinds of genes, constitutive and indu- 

 cible, exist in one cell after mating, and the dominant gene is the in- 

 ducible one. This inducible gene makes something, the repressor, 

 whereas the constitutive cell has no need for any inducer and, therefore, 

 presumably an inducer would not be part of a template. 



