Nucleic Acids and Nucleoproteins 65 



the genie substance it is probable that ehemical damage of 

 any kind will have some effect, but it is difficult to parti- 

 cularize as we do not know how the genetic information is 

 carried. If reduplication occurs by each base attracting its 

 complement as in the Crick and Watson scheme, it is clear 

 that loss of — NH2 or — OH groups by bases will prevent 

 their reduplication at this particular point. A break in a 

 nucleotide chain might make it impossible for the new particle 

 of DNA to be formed intact. However, it is not at present 

 certain that DNA duplication occurs in this way and there 

 are other possibilities in which some damage of the molecules 

 might be possible without impairing the genetic character. 

 It is noteworthy that Stent (1955) found that a considerable 

 amount of breakage of the nucleotide chains of phage could 

 occur without any loss of activity. 



It is difficult to see how the mere breakage of hydrogen 

 bonds between the nucleotide chains could cause permanent 

 genie damage as the reduplication, at least on the Crick and 

 Watson scheme, involves the separation of the two fibres, 

 unless the particle can only take part in the duplicating 

 process if it is intact and complete. It would be expected 

 that a small degree of hydrogen bond breakage could easily 

 be made good. This might possibly happen in some "reacti- 

 vation" processes. However, attempts to reactivate trypsin 

 which had been inactivated to the extent of 50 per cent by 

 irradiation in the solid state by exposure to ultraviolet, 

 infrared and heating at 100° were unsuccessful (Butler and 

 Philhps, 1956, unpublished experiments). It might, however, 

 be possible to reverse slight degrees of damage. 



It must also be remembered that the DNA is actually 

 present in somatic cells combined with histone. The histone 

 is known to be complex and to contain several substances of 

 different composition. However, since the total amount of the 

 bases present in the histone corresponds to at least 85 per 

 cent with the total amount of phosphate (Davison and Butler, 

 1956), it is reasonable to suppose that all or nearly all the 

 bases are attached to phosphate groups of DNA. We do not 



RAD. 4 



