BIOCHEMICAL STUDIES 123 



could involve first synthesis of a polypeptide chain— a process 

 not involving nucleic acid— then the adsorption of the polypep- 

 tide onto the nucleic acid of a chromosome, followed by contrac- 

 tion of the chromosome region concerned. The contraction would 

 fold the polypeptide-nucleic acid complex into a configuration 

 partly determined by the nucleic acid, and the folded protein 

 would then be shed from the chromosome. If this were so, it 

 would require that, in many cases at least, the genetically active 

 parts of chromosomes would be nucleic acids. Such a view stands 



Chromosome 



Histone nucleate 



Protein + ribose nucleic acid + histone 



Protein nucleate 



Fig. 7. To illustrate a simple system for protein synthesis, in which pentose 

 nucleic acid is acting as a trapping agent. 



in sharp contrast to the theory which regards genes as arrays of 

 enzymes. But it is easy to reconcile such a theory with the 

 species-specific actions of nucleic acids, and with the fact that 

 viruses (which many regard as analogous to genes) appear to 

 have no intrinsic enzymes but do have intrinsic nucleic acids. 



The second theory is that nucleic acid is a trapping agent. If, 

 by one means or another, an equilibrium is produced in a cell 

 between a protein and its precursors, then if the protein combines 

 with a trapping agent, which virtually removes it from the sys- 

 tem, further protein production must ensue. It is possible that 

 nucleic acids, through their well-known capacity to form com- 

 plexes with proteins, act as trapping agents. In such a case, dur- 

 ing active protein production, it would be necessary to produce 

 nucleic acid in proportion to the amount of protein produced. 

 This leads to a scheme such as that illustrated in Fig. 7 (Danielli, 

 1949). In this scheme a gene is conceived as a site of protein 

 synthesis and degradation, which is shifted in favour of synthesis 

 by the trapping action of pentose nucleic acid. The equilibrium 



