292 



Raymond Latarjet 



Latarjet, 1955, 1956). Attention will be called here briefly to 

 four points. 



(1) Inactivation. Non -aggregated DNA ("normal" TP), 

 obtained as the supernatant of a purified and centrifuged 

 preparation, when irradiated in frozen 10 per cent yeast 

 extract (direct effect), yields a typical broken inactivation 



100 

 90 



^? 40 - 



> 



I/) 



X 10 RADS 



Fig. 6. Direct X-ray inactivation of TP/sr. 

 1: Aggregated TP, preparation Bl ; 2: both preparations treated 

 with urea, and normal non-aggregated TP; 3: aggregated TP, 



preparation B2. 



curve (Fig. 6, curve 2). The majority of the units are inacti- 

 vated at a rate which corresponds to a target with a molecular 

 weight of about 5 X 10^. This is less than one-tenth the 

 weight of the whole DNA fibre, as measured by Dr. Doty on 

 the same preparation by light diff*usion. The other units 

 display such a high resistance that the corresponding target 

 would not include more than a few hundred nucleotides. 



