Nucleoside Triphosphate Pools and the Regulation of RNA Synthesis in E. coli

Amino acid starvation of "stringent RNA control" (RC^str) strains of Escherichia coli (E. coli) results in the cessation of net protein and net RNA synthesis, whereas "relaxed RNA control" (RC^rel) strains continue net RNA synthesis under the same conditions of amino acid starvation. This report tests further the hypothesis that net RNA synthesis is markedly reduced during amino acid starvation of RC^str strains as a result of reduction in the supply of substrates of the RNA polymerase. Bacterial ribonucleoside triphosphate pool levels were measured before and after the arrest of protein synthesis in RC^str and RC^rel strains. Protein synthesis was inhibited either by addition of trimethoprim to the medium or by the use of a mutant having a temperature-sensitive valyl-tRNA synthetase. The ribonucleoside triphosphate pool levels do not decline significantly during inhibition of protein synthesis in RC^str strains under either condition, and there is no apparent correlation between the measured pool levels and the residual rate of net RNA synthesis in RC^str and RC^rel strains. Thus, these data argue against the hypothesis that the regulation of RNA synthesis is mediated by the availability of substrates of the RNA polymerase.