284 Action of the Genetic Material 



quality. We have mentioned previously that many biochemical genet- 

 icists, including Beadle, have moved away from this specific quali- 

 tative theory as a general description of all genie actions and speak 

 more broadly of single functions controlled by the gene. Thus we have 

 not moved very far away from the old concepts, to which essentially 

 only one fact (a very important one, though) has been added: that 

 at one point in the gene-controlled determinative reactions a single 

 synthetic step for some substance is in some way, of many possible 

 ones, interfered with by the mutant action in cases which are acces- 

 sible to the deficiency-restoration type of experiment. 



A rather interesting discussion of this subject by Atwood and 

 Mukai (1953) emphasizes another aspect of the problem. They start 

 with the idea of indispensable functions, which are the ones knocked 

 out by the mutants in the deficiency experiments. They assume, how- 

 ever, that specific complex intermediates are shared by a fair number 

 of different enzymes or other large molecules. A mutation that affects 

 a single complex intermediate would affect the synthesis of a number 

 of different enzymes, leading to the loss of an indispensable function. 

 The detectable mutations would be confined to genes controlling the 

 final assembly of the complex fragments into macromolecules; thus 

 the total synthesis of an enzyme is not due to a single gene. Atwood 

 and Mukai think that medium-sized polypeptides are these intermedi- 

 ate gene products. These ideas are still well in line with Beadle's 

 one gene — one action concept, although, by emphasizing the inter- 

 mediate products and the interplay of genie actions, a bridge is made 

 toward the views to be discussed. 



It is interesting to compare my general attitude in the present 

 discussion with that of a biochemical geneticist who thinks that the 

 one gene — one enzyme theory is "manifestly unimportant, at the present 

 time" (D. M. Bonner, 1951). He points out that we have no criteria 

 for a primary genie function, that we cannot distinguish between one 

 or more gene-controlled primary effects, and that, therefore, the one 

 gene — one function idea "does not serve a useful purpose at the 

 present time." 



It is true, he further argues, that the biochemical reactions within 

 a cell are under nuclear control, since biochemical alteration has 

 inevitably been traced to genie alteration, but this tells us little about 

 the mechanism of genie control. Since the majority of cellular reac- 

 tions require participation of a specific enzyme, and since these 

 enzymes must be formed before the reaction takes place which they 

 catalyze, it is logical that the genes control the formation of enzymes. 



