Biosynthesis of Pyrimidines 



161 



Table IX 

 DNA Components of Bacteria 



nucleic acid. We report the incorporation in DNA pyrimi- 

 dines. The RNA has been shown to be completely inert in 

 the infected cell. DNA cytidylic acquired slightly more 

 specific radioactivity than did thymidylic acid. 



These bacteria were then washed, suspended in a non- 

 radioactive medium and infected with virus. The problem we 

 wished to study was this: Do the virus particles which are 

 synthesized early receive a greater proportion of host DNA 

 than those formed later, or do all particles receive a constant 

 proportion of material from host DNA and medium? Three 

 portions of virus were prepared. Some bacteria were infected 

 with T6r virus which caused lysis of bacterial cells after 

 35 minutes. Two other portions of radioactive bacteria were 

 infected with T6r+ virus. One portion was allowed to lyse 

 the cells naturally (this started in 90 minutes) and the other 

 portion was treated with cyanide after 35 minutes. This 

 caused cessation of metabolism and lysis of bacterial cells. 



The amount of newly formed DNA in the virus was deter- 

 mined in each case. The values are found at the bottom of 

 the table. The smallest amount of DNA formed is associated 



ISOTOPES 



12 



