Stimulation of enzyme synthesis by sublethal concentrations of chloramphenicol is not mediated by ribonucleotide pools.

Growth of Salmonella typhimurium LT-2 strain pyrA81 in minimal medium containing 0.8 mug of chloramphenicol (CAP) per ml resulted in a 50 to 100% increase in the steady-state nucleotide pools in the cells. When such a culture was starved for uracil, the pyrimidine nucleotide pools decayed much more slowly in CAP-treated cells than in controls. An attempt was made to determine whether this effect of CAP on nucleotide pools could account for enhanced enzyme derepression observed under the same conditions (8). Treatment with low levels of puromycin also resulted in elevation of nucleotide pools but did not lead to enhanced enzyme synthesis. CAP treatment during arginine starvation has been shown to enhance enzyme synthesis, but nucleotide pools were not significantly affected by CAP nor was the stringent response relieved under these conditions. Thus, the effects of CAP on enzyme synthesis cannot be the result of effects of the antibiotic on nucleotide pools in all cases. The elevation of nucleotide pools was shown not to be due to enhanced conversion of exogeneous uracil into nucleotides, but to result from the enhanced turnover of ribonucleic acid in CAP-treated cells.