58 



KOZLOFF ET AL. 



TABLE II 

 KINETIC STUDY OF THE SOURCES OF VIRUS NITROGEN 



Atom % excess N^° in virus N 

 Atom % excess N^° in bacteria prior to infection 



derived from an exhaustible substrate. On the other hand, although 

 the standard medium contains only 0.01% NH4CI (the minimal 

 amount for good phage growth in resuspended bacteria), raising the 

 N content of the medium over a 10-fold range or supplementation of 

 the medium gave no clear effect on either the isotope degree of incor- 

 poration or the distribution of the isotope in the phage. 



Host N^^ was found in all the substances isolated from the phage: 

 protein, nucleic acid, the adenine, guanine, thymine, and cytosine of 

 the nucleic acid, and the acidic, basic and neutral amino acid fractions 

 of the hydrolyzed protein. No significant difference appeared in the 

 isotope distribution in the three amino acid fractions, but significant 

 differences were noted in the distribution of N^^ among the purines 

 and pyrimidines. As shown in Table III guanine was labeled to a 

 greater extent than adenine. The high incorporation in the thymine 

 is noteworthy since bacterial DNA is the only appreciable host source 

 of this base. 



The simultaneous transfer of bacterial N and P to phage nucleic 



