STUDIES ON MECHANISM OF SYNTHESIS OF SOLUBLE RIBONUCLEIC ACID 121 



4. The effect of snake venom phosphodiesterase 



If S-RNA-^ plus -y is treated with snake venom phosphodiesterase 

 under conditions of limited degradation, a somewhat random degradation 

 occurs as evidenced by the fact that p-P]-CTP attaches to a variety of 

 terminal groups (Table V), as contrasted to its attachment to cytidylic 



TABLE V 



The Site of Attachment of ['-P]-CMP on Native and Pyrophosphorvlvzed 



S-RNA 



Radioactivity in the 2' (3')-ribonucleoside mono- 

 phosphates isolated after alkaline hvdrolysis of 

 the 32p.S-RNA 



Results expressed as per cent of total c.p.m. 

 incorporated 



AMP CMP UMP GMP 



Native S-RNA 



(o-o /^moles P-P, 



2-0 |uatoms Mg) <5 90 S-io <s 



P-P-treated S-RNA 



(i -o /xmoles P-P, 



20^molesMg) 15 85 <5 <s 



P-P-treated S-RNA 



(4-0 /^imoles P-P, 



8 • o /^imoles Mg) 48 50 < 5 < 5 



Phosphodiesterase 



treated S-RNA 20 55 11 14 



S-RNA-/S and -7 was incubated with the ribonucleotide-incorporating enzyme 

 under standard conditions and with the amounts of pyrophosphate and Mg + + 

 indicated within parentheses above. The fourth sample of S-RNA was pre- 

 treated with phosphodiesterase. The various S-RNA preparations were then 

 extracted and incubated with [^'^P]-CTP (^-P-P-P) and the ribonucleotide-in- 

 corporating enzNTTie under standard conditions. At the end of the incubation each 

 S-RNA was isolated, hydrolyzed with alkali and the radioactivity in the various 

 ribonucleotide fractions determined. 



acid alone when native S-RNA is the substrate or to cytidylic acid and 

 adenylic acid when pyrophosphorylyzed S-RNA is the substrate. 



The experiment summarized in Table VI was designed to establish 

 whether, after degradation of the S-RNA by snake venom phosphodies- 

 terase to such a degree that its ability to accept amino acids is lost, it is 

 possible to restore this ability by re-incorporating ribonucleotides into 

 the partly degraded S-RNA. 



