322 A. C. R. Dean and Sir Cyril Hinshelwood 



hydrogen bonds joining the parallel helices would be con- 

 siderable, and maintains that a similar criticism would apply 

 to the mechanism of Delbrllck (1954) whereby the chains are 

 separated and later recombined by a series of breaks and 

 reunions in a zipper-like fashion. Arley states that Gamow's 

 suggestion (1954) of a one to one correspondence between the 

 double polynucleotide chain of a DNA molecule of the 

 Watson-Crick type and the single polypeptide chain of a 

 protein (or enzyme) molecule of the Pauling and Corey (1951a 

 and b) type, leads to a simpler mechanism. In it the linear 

 information contained in the DNA molecule is translated one 

 to one into that of a protein molecule, each of the possible 

 (about 20) quadruples of purines and pyrimidines correspond- 

 ing to one of the possible (about 20) amino acids. Since the 

 correspondence is one to one Gamow has shown that a protein 

 (or enzyme) molecule can be built up "on the inside" of the 

 double helix of a DNA molecule so that the order of the 

 amino acids is uniquely determined by the order of the 

 purine-pyrimidines. This new protein molecule can now 

 serve as a template for the building up of a DNA molecule 

 "around" the protein molecule as axis so that the order of 

 the purine-pyrimidines is now uniquely determined by the 

 order of the amino acids. 



Another model involving the participation of protein in 

 DNA rephcation has been proposed by Butler (1956). In it the 

 twin fibre of DNA is closed at one end and the single fibres 

 are attached to hist one at the other end. A pull on the his tone 

 fibres will separate the two strands of the DNA (zipper 

 fashion) and at the same time uncoil the spiral. It is supposed 

 that the DNA fibre replicates in the open position and that 

 another pull on the histone fibres in the middle will cause each 

 to close up. If this is correct each new DNA particle formed 

 will be made of newly synthesized material. 



Whichever of these theories is correct it seems likely that 

 proteins and nucleic acids are intimately interconnected in 

 the cell and the evidence that nucleic acid is concerned in 

 protein synthesis has recently been reviewed by Gale (1958). 



