68 Information Storage and Neural Control 



numbers will be quite different, and assuming that 3U is the code 

 for phenylalanine). 



The way to complete the determination of the genetic code by 

 discovering the actual sequence of bases is also clear in principle 

 using the biochemical approach. It should be possible to add 

 small, known ribonucleotide sequences to poly U enzymatically 

 and to use these messengers to produce polyphenylalanine plus 

 the amino acids coded by these sequences (if any). Unless there are 

 some large surprises lurking around the corner, the genetic code 

 for E. coll may well be officially solved within the next three 

 years or so. There remains the question of whether the coli code 

 is common to all organisms, although most of the limited infor- 

 mation available argues for universality. Even if the code is 

 different in higher organisms, the techniques evolved for the coli 

 system should be generally applicable. All that is needed is a 

 crude, cell-free, protein-synthesizing system plus the proper syn- 

 thetic messenger to trick the system. 



CONTROL OF THE RATE OF PROTEIN SYNTHESIS 



(The Regulatory Problem) 



The process by which genetic information is converted into 

 protein specificity is rapidly becoming spelled out, and the com- 

 plete unraveling of the exact nature of the genetic code providing 

 this specificity of protein structure is on the horizon. However, 

 the genetic control necessary to provide for the adaptive skill of 

 the microorganism and for the much more complicated growth 

 pattern of the differentiated organism cannot be accounted for 

 simply by the ability of genes to control protein structure. The 

 structural gene, structural messenger, and ribosome constitute a 

 protein factory, always working at the same rate for all proteins. 

 It seems obvious that there must exist regulatory genes involved 

 in turning on and off the structural genes and in varying the 

 enzyme complement of the cell. 



Recent work with bacteria has shown the existence of genes 

 which serve to control the rate of protein synthesis in response to 

 changes in external conditions. Normally, the production of the 

 lactose-hydrolyzing enzyme ^-galactosidase by the bacterium 



