[Dependence of threonine operon expression on the relA gene allelic state and the level of guanosine tetraphosphate in E. coli].

The expression of threonine operon in Rel+ and Rel- E. coli cells was studied at the transcriptional level. The rel+ genotype and the lack of a specific amino acid--threonine--are necessary for the stimulation of threonine operon transcription. Under these conditions the RNA fraction, which is thr-mRNA, is increased 2-fold. The lack of arginine or histidine in Rel+ strain does not lead to derepression of the threonine operon. It is shown that in a cell-free system 0.1 mM ppGpp stimulate the synthesis of thr-mRNA on phage DNA lambda dthr and plasmid DNA PYN1107, containing total threonine operon 1.5--2-fold. It is assumed that ppGpp stimulates the initiation of transcription. Studies on the strain carrying spoT- mutation, which significantly lowers the rate of ppGpp degradation and results in suppression of rel- phenotype, revealed positive correlation between the intracellular level of ppGpp and the thr-mRNA fraction in the total transcript.