[Metabolic regulation of threonine operon transcription in E. coli cells].

The threonine biosynthetic operon transcription in E. coli cells during balanced growth was studied. The rate of threonine-mRNA synthesis was measured by hybridization of impulse-labelled RNA with pYN 1107 DNA carrying the structural threonine genes A, B, C. It was shown that threonine-mRNA synthesis depends on bacterial growth rate being maximal at mu = 0.8 doublings per hour. The influence of the ppGpp on the bacterial growth rate and threonine-mRNA synthesis rate was demonstrated, using spoT-mutants and strains with several relA gene copies. The rate of threonine-mRNA synthesis is maximal at the ppGpp level of about 50-60 pmole/A450. The deviation from this ppGpp optimum level results in inhibition of the threonine-mRNA synthesis. Thus, ppGpp appears to be involved in metabolic regulation of operon transcription. A mechanism of negative regulation of threonine-mRNA synthesis by high concentrations of ppGpp is discussed.