STUDIES ON MECHANISM OF SYNTHESIS OF SOLUBLE RIBONUCLEIC ACID II J 



diphosphate is the only diphosphate which can be found. S-RXA-^ is 

 rich in the molecular species which terminates in adenylic acid (yielding 

 adenosine upon alkaline hydrolysis) and has no detectable S-RNA species 

 terminating in uridylic acid. S-RXA-y is rich in the molecular species 

 which terminates in guanylic acid and has some of the molecular species 

 which terminates in uridyHc acid. 



The ribonucleotide analyses of these two families of S-RNA indicate 

 that approximately one pseudouridylic acid molecule corresponds to one 

 chain (Table II). In addition, the adenylic acid content of S-RNA-^S 



TABLE II 

 Composition of S-RNA-^ and S-RNA-y 



* Molar composition calculated by assuming that one terminal ribonucleoside 

 residue corresponds to one polynucleotide chain. Chromatographic analysis made 

 on the alkaline hydrolysates of S-RNA-^ and of S-RNA-y. 



t Including one of the nucleoside end and one guanosine diphosphate. 



and of S-RNA-y approximates the sum of uridylic acid plus pseudouridylic 

 acid whereas the guanylic acid content approximates that of cytidylic 

 acid. From the end-group analysis (assuming one end-group per chain), a 

 molecular weight of approximately 15 000 can be derived. 



3. The effect of pyrophosphate 



Incubation of the enzyme with S-RNA-/3 plus -y, [^^C]-CTP, in- 

 organic pyrophosphate and Mg ' ^, results in an enhanced incorporation 

 of P^C]-CMP into the S-RNA (Table III). This effect can also be ob- 

 served if the enzyme and the S-RNA are preincubated with inorganic 

 pyrophosphate, the S-RNA then extracted and reincubated with a fresh 

 enzyme preparation and [^^C]-CTP in the absence of pyrophosphate. It 



