CYTOPLASMIC INHERITANCE 



27-14 



thesis of more enzyme. As more galactose is broken down more 

 energy becomes available for the production of more galactozy- 

 mase and the synthesis of enzyme takes place at a constantly in- 

 creasing rate. 



Monod follows this destructive criticism of the plasmagene 

 hypothesis with a constructive hypothesis of his own. He proposes 

 a scheme by which an autocatalytic process of enzyme synthesis 

 could occur without the existence in the cytoplasm of autonomous 

 entities. This scheme makes it unnecessary that autonomous gene 

 replicas be released into the cytoplasm. In Monod' s view, the 

 gene might simply produce a specific substance B (fig. 27-5) 

 which could imite in the cytoplasm with inactive (presumably pro- 

 tein) units and these when stabilized by the specific substrate 

 (e.g. galactose) could catalyze their own polymerization. This 

 produces an autocatalytic process without the production of an 

 autonomous substance by the gene. Monod' s B substance corres- 

 ponds to the gene -product ribosenucleic acid complex in my 

 scheme of gene action shown in fig. 28-1. It is the small mole- 

 culed specificity-conferring substance to which I have previously 

 referred as the substance by which the gene exerts its effects. 







A 



I 



I 



A 



L 



L 



> 



G. 



B 



+ 2 L 



» E. 



+ S 



■^ 5 E, 



+ B+21 



» 5L. 



--> 



Fig. 27-5 Tentative Scheme of Gene Controlled, Autocatalytic 

 Enzyme Synthesis. Gj = gene; Bj = "specific building blocks" 

 manufactured by gene; i = non-specific building blocks; S = sub- 

 strate; i-B-i aggregates = active enzymes. (Copied from Monod.) 



My objections to the plasmogene hjrpothesis have been strong- 

 ly supported by Marshak's recent work. His demonstration that a 

 nuclear nucleic acid is the precursor for both desoxyribose 

 nucleic and ribosenucleic acids proves that both these substances 

 originate from the nucleus and negates the plasmagene hypothesis. 



