STUDIES ON THE INCORPORATION OF ARGININE 



303 



Since the arg.R~ strain 30SQA5 was originally isolated as a canavanine- 

 resistant mutant [5], a comparison was made of the canavanine inhibition 

 of the arginine-activating enzymes isolated from 308^ and from 30S0A5. 

 About 3 • 3 fjig. of purified activating enzyme was used in each assay and 

 the canavanine concentration was varied over a twentyfold range. The 

 results from these experiments (see Fig. 2) show no difference in the 

 sensitivity between the enzymes from the two strains. 



CHARACTERIZATION OF THE ARGININE-RNA 



A comparison was made between the acceptor RNA from the wild 

 type and the arg.R~ mutant, using 15 fig. of the same preparation of 

 purified arginine-activating enzyme in each assay. Figure 3 shows the RNA- 



10 15 20 25 



Optical units s-RNA 



Fig. 3. RNA dependence for the formation of arginine-RNA. Acceptor RNA 

 from strain 30S0 (wild type) represented by open circles, from strain 30S0A5 (the 

 arg . R-mutant) denoted by filled circles. 



dependence for the formation of arginine-RNA. The slopes of the lines 

 correspond to an uptake of i arginine per 1900 nucleotides for the wild 

 type and i arginine per 1200 nucleotides for the arg.R" mutant. Figure 4 

 shows the enzyme dependence of the formation of arginine-RNA for 

 a pair of RNA preparations other than those used for the experiments of 

 Fig. 3. At all levels of enzyme, the amount of arginine-RNA formed in 

 1 5 min. is larger in the arg . R~ mutant than in the wild type. To test whether 

 or not the difference observed in the two previous experiments was specific 

 for arginine, the incorporation of arginine was compared to that of the 

 amino acid mixture (which contains about 6% arginine). Table II shows 



