142 S. S. COHEN 



proteins also have marked similarities in primary structure and serological 

 cross-reactivities (Cohn, 1954). Thus, as has been suggested, the cell may be 

 producing a fixed polypeptide, whose secondary and tertiary structure may 

 be determined by the presence of antigen in one case, and inducer in another. 



However, Schweet and Owen (1957) have recently summarized the similar- 

 ities and differences between inducible biosynthesis and antibody production. 

 They have stressed particularly the observed penetration of antigens into 

 nuclei and have suggested that antigen modifies the genetic apparatus of 

 cells capable of producing globulins. These cells on duplication produce new 

 genetic codes, new templates which direct the synthesis of new globulin 

 configurations. In these senses, then, antibody production may be more 

 closely related to some types of virus production, since data have been 

 obtained to indicate that the RNA viruses of influenza and poliomyelitis also 

 stimulate marked nuclear changes, reflected in alterations of DNA meta- 

 bolism. 



Spiegehnan and his collaborators (1955) have studied the problem of the 

 nature of intermediates between amino acids and enzymes. They have shown 

 that a single amino acid analog wliich blocks enzjone synthesis does not 

 produce an accumulation of endogenous peptides in the microorganisms or 

 the incorporation of other amino acids to cell structure. They have concluded 

 that the first stable mtermediate on the way to protein synthesis requires the 

 simultaneous presence of a large number of different amino acids. The 

 impHcation is therefore clear that protein synthesis does not involve a 

 stepwise formation of larger and larger peptides, the formation of each of 

 which requires its own. specific catalyst. 



3. Role of Nucleic Acids in Inducible Systems 



Enzyme synthesis in inducible systems, even as protem synthesis in 

 general, is intimately tied to the presence and synthesis of nucleic acid. 

 However, it is not yet known whether the presence of DNA is or is not 

 required for induced biosynthesis to take place. That DNA synthesis is not 

 essential to the induced biosynthesis has been indicated by the following 

 evidence: 



a. X-irradiation of yeast and ultraviolet irradiation of yeast and bacteria 

 in quantities sufficient to block DNA synthesis without affecting RNA and 

 protein synthesis does not affect the induced biosynthesis of enzymes (Baron 

 et at., 1953; Halvorson and Jackson, 1956). 



b. A thymineless mutant of E. coli can synthesize various inducible 

 enzymes, ENA, and protein in the absence of exogenous thymine and of a 

 significant synthesis of DNA (Cohen and Earner, 1954). 



c. E. coli, treated with mustard gas, cannot make DNA but can be induced 

 by lactose (Eardee, 1954). 



