62 THE BIOSYNTHESIS OF PROTEINS 



here a very interesting aspect of the regulation of bacterial protein 

 synthesis. 



A direct attempt was made by Jacob and Pardee (1959) to find out 

 whether genetic DNA participates in making the corresponding protein. 

 They studied the kinetics of ^-galactosidase appearance in bacteria which 

 originally lack the corresponding gene, when the gene is introduced by 

 bacterial conjugation. It was shown that the enzyme is produced at the 

 maximal rate within a few minutes, and possibly immediately after the 

 introduction of the piece of genome containing the competent gene. More- 

 over, the amount of j8-galactosidase synthesized in a population of such 

 zygotes is proportional to the square of time. This can be interpreted in the 

 following way: as the number of zygotes formed is known to be propor- 

 tional to time, the production of protein molecules must again be directly 

 proportional to the time elapsed after zygote formation for the experi- 

 mental quadratic function to be satisfied. This is exactly what one would 

 expect if the gene would act directly as a catalyst in the production of the 

 protein. If the gene were producing a stable intermediary catalyst at a 

 constant rate, which in turn would make the enzyme at a constant rate, the 

 enzyme production would be a function of the third power of time. The 

 experimental data are therefore incompatible with the continuous pro- 

 duction at a constant rate under the action of the genetic locus of a stable 

 catalyst which in turn produces enzymes linearly (Jacob, 1959). They could 

 not, however, be taken as evidence for the direct participation of DNA in 

 the making of j8-galactosidase. A few minutes is a long time for E. colt; 

 which is able to make a protein within 5 sec (McQuillen et al., 1959) and 

 very complex processes may take place within the 5 min or so which follow 

 conjugation. It is conceivable that some stable catalyst is being made 

 rapidly in a limited number of samples during this period. Another pos- 

 sibility is that an unstable agent is produced continuously in the presence 

 of DNA only. 



3. Conclusion 



There is no positive evidence at present for a direct participation of DNA 

 in protein synthesis in any of the systems studied so far. On the other hand, 

 there is ample and clear evidence that many proteins can be made without 

 the direct participation of DNA. 



This raises a fundamental question. If DNA carries coded information 

 concerning the primary structure of proteins, and if its presence and inte- 

 grity are not a prerequisite of protein synthesis, it must be concluded that 

 the genetic information is transferred from DNA to some other cell con- 

 stituent in which it can be preserved for some time and eventually used in 

 protein synthesis. This is a logical necessity. But no one knows to what 

 substance the information is transferred, neither in what form, nor when 



