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E. S. CANELLAKIS AND EDWARD HERBERT 



The combined S-RNA-^ and -y was partly degraded with snake 

 venom phosphodiesterase. The partly degraded S-RNA was incubated 

 with the ribonucleotide-incorporating enzymes, in the presence of the 

 non-radioactive ribonucleoside triphosphates listed in Table VI. At the 

 end of 10 min. the amino acid-activating enzyme was added to each tube 

 together with radioactive threonine and the capacity of the S-RNA to 

 accept a radioactive threonine was measured. 



TABLE VI 



Reconstitution of the Capacity of S-RNA-^ and -y to Accept Threonine 



The phosphodiesterase treated S-RNA was prepared by treatment of the 

 S-RNA with snake venom phosphodiesterase, and was then isolated free of the 

 phosphodiesterase. The pretreatment of the S-RNA was carried out as follows : 

 0-15 ml. of S-RNA-/3 and -y (Eogg = 40) were incubated with the equivalent amount 

 of ribonucleotide-incorporating enzyme (0-15 ml.), i /itmole of MgCli, 0-25 

 /xmole of the indicated ribonucleoside s'-triphosphate in o-o8 M potassium 

 phosphate buffer, pH 72; the total volume was 0-5 ml. After incubation for 15 

 min. at 37°, 0-5 ml. of a mixture containing 0-2 ml. of the amino acid activating- 

 enzyme fractions, 0-05 /xmole of [^*C] -threonine (35 x lo*^ c.p.m.//xmole), 4 

 /Limoles of ATP and 2 /xmoles MgClo, all in the o-o8 m potassium phosphate buffer, 

 were added to each tube and the incubation was continued for 10 min. more at 

 37' . The S-RNA was then isolated, freed of contaminant radioactivity and counted. 



Degradation of the S-RNA with phosphodiesterase results in a decrease 

 in its capacity to accept threonine. If the degraded S-RNA was pretreated 

 with the ribonucleotide-incorporating enzyme and ATP, a further decrease 

 in its capacity to accept threonine was noted. In contrast to this, when pre- 

 treatment was carried out in the presence of ATP and CTP, the capacity 

 of the degraded S-RNA to accept threonine was greatly enhanced. Pre- 

 treatment with ATP, CTP and UTP further enhanced the ability of the 

 S-RNA to accept threonine, and finally, pretreatment of the S-RNA with 



