122 CYTOCHEMISTRY OF PROTEINS 



shown that type changes in bacteria were mediated only by the 

 action of the nucleic acids of that species. Further evidence was 

 obtained by Mazia, who showed that nucleic acids block the de- 

 velopment of fertilised sea-urchin eggs and that the action is 

 markedly dependent upon the species from which the nucleic 

 acid is obtained. Horstadius, Lorch, and Danielli also injected 

 nucleic acids into sea-urchin eggs, and obtained activation which 

 was to a considerable degree dependent upon the source of the 

 nucleic acid. It is therefore clear that any theory of the role of 

 nucleic acid must provide for a considerable degree of species 

 specificity. This, however, can be done in a variety of ways. 

 Two such mechanisms which will be discussed here are (1) that 

 nucleic acids are folding agents and (2) that nucleic acids are 

 trapping agents. 



The first of these theories is based upon the fact that the 

 natural proteins of cells consist not merely of a specific peptide 

 chain but of a peptide chain which is folded into a specific con- 

 figuration. Treatment of natural proteins with so-called de- 

 naturing agents, which cause a loss of this specific configuration, 

 causes a loss of biological activity and even a marked loss of 

 ability to react with antibodies to the original natural protein. 

 Thus the unique configuration of a natural protein is funda- 

 mental to its normal action. But these unique configurations 

 cannot be produced without some highly specific mechanism. 

 May it not be that the steric factors in this mechanism are pro- 

 vided by nucleic acids? Astbury has pointed out that the dis- 

 tance between nucleotides in nucleic acids closely corresponds to 

 the distance between peptides in a polypeptide chain, so that a 

 precise adlineation between protein and nucleic acid is possible. 

 If now the mechanical properties of the nucleic acid are such as 

 to facilitate a particular manner of folding, we can picture a 

 process in which a polypeptide adsorbs on a nucleic acid mole- 

 cule, is folded into a unique configuration by folding of the 

 nucleic acid, and is then shed as a folded globular protein. This, 

 of course, leads to the question, what folds the nucleic acid? 

 The reply to this may well reside in a possibility considered in 

 Chapter 3, namely, that the chromosomes, in their active regions, 

 are constantly folding and unfolding, through the action of phos- 

 phate esters upon a phosphatase-contractile protein unit in the 

 chromosome. Thus the complete picture of protein production 



