196 S. S. COHEN 



B. The Transfer of Biological Information 

 1. DNA as a Template 



How is the code contained within DNA used as a template for the syn- 

 thesis of RNA and pro tern? It has been seen that protamines and histones 

 may wrap around DNA in such a way as to suggest a selection of residues 

 which wiU fit the grooves made available in the helical coil. The closeness of 

 fit w^hich this complementarity requires is not clear; no evidence for the 

 biological specificity of protamines or histones has yet been obtained. In 

 any case, there appears to be a synthesis and turnover of these basic proteins 

 to an extent no greater than that of DNA, and the chromosomal location of 

 these substances would seem to Hmit their utility in extending the control of 

 genetic material to the physiological sites. 



It has been seen that a third strand of RNA may form a triplex within a 

 duplex of RNA, and it has been suggested that the synthesis of specific RNA 

 occurs in this manner w^ithin the duplex of DNA at the chromosome site. 

 Such a hypothesis is usually extended to imply that the nuclear genetic 

 substance (DNA) controls the production of RNA in the nucleus, which then 

 determines the synthesis of essential proteins in other parts of the cell, 

 notably in the cytoplasm. 



This mechanism of RNA synthesis does not necessarily require a con- 

 comitant synthesis of DNA during the reproduction of the carriers of physio- 

 logically useful information. One particularly good case in support of this 

 concept is known in the work of Watanabe (1957) on the control of synthesis 

 of phage protein. If T2-infected bacteria are irradiated with ultraviolet light 

 a few minutes after infection and insertion of phage DNA, DNA synthesis 

 does not occur but the synthesis of phage antigens contiimes. Initial irradia- 

 tion of phage or uifected bacteria eliminates the abihty to synthesize these 

 proteins. Thus, the information necessary for protein synthesis has been trans- 

 ferred to some unit of lower sensitivity to ultraviolet irradiation than has 

 phage DNA, and this transfer occurs before the duphcation of DNA. 



In general, it is supposed that the use of DNA as a template will require 

 the complementarity or closeness of fit discussed, for example, in connection 

 with the Watson-Crick model or by Pauling (1955) and other workers in 

 considering antigen-antibody reactions and antibody synthesis. These may 

 lead to the formation of complementary nonidentical structures, such as the 

 strands of DNA, and possibly to the formation of complementary identical 

 structures, as in the aggregation of chains of polyadenyHc acid which hydro- 

 gen bond through adenine moieties, leading to a restriction of resonance and 

 ultraviolet absorption of these residues. The latter mechanism has been dis- 

 cussed, not only by Donohue and Stent (1956) for RNA, but had been pro- 

 posed many years earher in connection with possible mechanisms of protein 



