650 H. O. HALVORSON 
imposed either through exhaustion of nutrients, by resuspending cells in deficient 
medium, or by the use of selective inhibitors lead to both RNA and protein degrada- 
tion. Table II summarizes some of the methods employed. In many cases both 
RNA and protein breakdown have not been followed in the same system. It is 
clear that imposing conditions which lead to unbalanced synthesis favor intra- 
cellular breakdown. For example, BARNER AND COHEN?® showed that when FE. colt 
strain 15Z;_j— was incubated in the absence of pyrimidines, protein synthesis con- 
tinued coupled with an increased turnover of RNA. 
One would expect that if intracellular turnover was dependent upon the de novo 
synthesis of an essential degradative enzyme(s) that its production should be depen- 
dent upon protein synthesis. The data summarized in Table II argue against this 
TABLE ft 
METHODS FOR INITIATING BREAKDOWN AND TURNOVER 








Degradation 
Conditions employed = Reference 
Protein RNA 
Starvation 
Carbon + a. 6 
Nitrogen a. 4. on23} 
Specific amino acids -+ -- 2, Wit, Bel 
Sporulation + 25 
Pyrimidines + 26 
Mg?t + 27 
Phosphate = 28 
Inhibitors 
Penicillin ale 10 
Amino acid analogs + 29 
Phage infection a + 30 
hypothesis. When rapidly growing cells are incubated under conditions restricting 
protein synthesis (nitrogen and amino acid starvation; in the presence of amino 
acid analogs), protein breakdown ensues. Since a limited synthesis of protein 
might take place during the starvation of the intracellular amino acid pool, such 
observations do not directly rule out the protein synthesis hypothesis. Chloram- 
phenicol, which immediately blocks protein synthesis was shown by MANDELSTAM® 
to have no effect on the rate of protein breakdown in FE. coli during leucine starvation. 
After 90 min a progressive inhibition of protein breakdown was observed in the 
presence of chloramphenicol which is probably due to an indirect effect. HANCOCK*" 
observed a chloramphenicol-induced accumulation of pool amino acids in Staphylo- 
coccus aureus, however, it is not clear in this case to which extent the free amino 
acids are derived from cellular proteins. Finally, dosages of ultraviolet light, which 
inhibit protein synthesis, lead to an increase in the free amino acid pool of yeast via 
protein breakdown*?. 
References p. 653/654 
