272 



HEINZ SCHUSTER 



1.0 



40 60 80 

 Time (mln.) 



Fig. 7. Survival curves of TMV-RNA heated at pH 7.15 in 0.1 M phosphate buffer 

 [W. Ginoza, Nature 181, 958 (1958).] 



of RNA hydrolytically, cause a simultaneous inactivation of the nucleic 

 acid molecule, as has been shown with ribonuclease. Ribonuclease splits the 

 ester bond between phosphoric acid and carbon atom 5' of ribose, but only 

 if the adjacent nucleotide to which phosphoric acid is esterified at carbon 

 atom position 3' is a pyrimidine nucleotide. In contrast, snake venom 

 phosphodiesterase splits the ester bond between phosphoric acid and carbon 

 atom 3' of ribose, so that this enzyme must also cause an inactivation of 

 RNA (compare Chapter 15). 



Reddi 92 has studied the degradation products obtained by treating TMV- 

 RNA with a purified phosphodiesterase from Micrococcus pyogenes var. 

 aureus. The 3 '-phosphates of all four nucleotides were found along with 

 numerous dinucleotides of the general configuration, nucleoside-3',5'- 

 nucleoside-3 '-phosphate. This enzyme, which also degrades DNA to nucleo- 

 tides, must, therefore, hydrolytically split phosphoric acid from the carbon 

 atom 5' of ribose; it does not act on purine or cyclic pyrimidine nucleotides. 

 Chromatographically purified phosphomonoesterase, 93 which is free from 

 diesterase activity, has no effect on the biological activity of TMV-RNA 



92 K. K. Reddi, Nature 182, 1308 (1958). 



93 H. G. Bomann, Biochim. et Biophys. Acta 16, 245 (1955). 



