70 Information Storage and Neural Control 



indicated that a gene involved in the regulation of this enzyme 

 can hav^e a positive effect, i.e., can be involved in turning on a 

 gene to its full capacity. Therefore, the generality of the model 

 proposed for the /3-galactosidase system is not at present estab- 

 lished; but the essential feature of the model — the proposed 

 existence of specific gene products which exert a controlling 

 influence over the rate of synthesis of the structural messenger 

 RNA — is very appealing. It serves as a valuable guide to future 

 experimental efforts aimed at trying to understand the control 

 process at a chemical level. 



CONCLUDING COMMENTS 



We have considered: 1) the chemical nature of the gene; 

 2) the "sequence hypothesis" which serves as the basis for our 

 definition of the genetic coding problem; 3) the evidence sup- 

 porting the sequence hypothesis from combined genetic and 

 chemical studies; 4) the recent rather dramatic progress of the 

 biochemical approach; and, finally, 5) the problem of regulation. 

 We cannot at present unequivocally separate fact from fancy. 

 However, the evidence now extant certainly favors our main 

 conclusions: 1) that the genetic information of an organism is 

 contained in the base sequence of its DNA; 2) that the base 

 sequence of the DNA of "structural genes" specifies the amino 

 acid sequence of proteins; 3) that an RNA "messenger" carries 

 the genetic information from the structural gene to the ribosome 

 for protein synthesis; and, finally, 4) that the base sequence of 

 the DNA of certain "regulator genes" specifies a material which 

 exerts a controlling influence over the rate of protein synthesis. 

 It should be emphasized, however, that most of the evidence for 

 these conclusions comes from work with microorganisms and that 

 the generalization to higher organisms is chiefly an act of faith. 



REFERENCES 



1. Horowitz, N. H.: Biochemical genetics of neurospora, Advances in 



Genetics, J.' 33, 1950. 



2. Levinthal, C: Coding aspects of protein synthesis. Revs. Mod. Physics, 



J7.-249, 1959. 



