S. S. COHEN 



301 



fraction contained essentially no radioactive P. It may be concluded from 

 this experiment and others which yielded the same result that not more 

 than 2 per cent of the RNA could have been imdergoing synthesis involving 

 P of the medium. It is highly improbable that the turnover of this much 

 RNA, if any synthesis actually occurred, could have produced the synthesis 

 of the DNA found. Therefore it appears that RNA nucleotides are not 

 precursors to DNA synthesis in this system. 



Since special precautions were not taken to purify the nucleotides of the 

 RNA fraction before estimating the radioactivity, it is possible that even 

 the low radioactivity found (2 per cent) was due to some contaminant, and 

 was not truly significant. In this experiment the lipide P was found to 

 have a radioactivity of about 26 per cent of the P of the medium. Repre- 

 cipitation of phospholipide in the presence of carrier sphingomyelin derived 



Table IV 

 Inclusion of Radioactive P into Nucleic Acids of Escherichia coli B Infected with T'2r+ 



Bacteriophage 



DNA, counts corrected for presence of original bacterial DNA; RNA, counts cor- 

 rected for presence of traces of DNA in RNA fraction. 



from beef lung readily reduced the radioactivity sufficiently to suggest the 

 inactivity of the phospholipide fraction. 



Fractionation of Non-Protein P — It was not found possible to isolate or- 

 ganic phosphate from the TCA supernatant fluids in this experiment, owing 

 to the large excess of inorganic P of the medium. In another experiment, 

 the bacteria were first sedimented to remove the inorganic P of the medium 

 before fractionation. 10 cc. of TCA extract contained 66 7 of organic P 

 and 183 7 of inorganic P. To this solution, adjusted to pH 8.3 with 

 NH4OH, were added 1 cc. of 2.5 per cent CaCl2 and 2 cc. of a 0.5 per cent 

 suspension of MgCOs. After being chilled, the mixture was centrifuged and 

 the sediment was discarded. The supernatant fluid was precipitated with 4 

 volumes of alcohol and stored overnight in the ice box. The alcohol precipi- 

 tate was placed in 3 cc. of water. It contained 44 7 of organic P, of which 

 ribose-5-phosphate in some form comprised 75 per cent of the total organic 

 P of the fraction (10). The water-soluble fraction of the alcohol precipi- 

 tate contained 16.5 7 of pentose P in 25 7 of organic P. The radioactivity 

 per microgram of P of this fraction was 37 per cent of that of the inorganic 



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