Selective inhibition of transcription of the E. coli tufB operon by guanosine-5'-diphosphate-3'-diphosphate.

We have studied the effect of guanosine-5'-diphosphate-3'-diphosphate (ppGpp) on the transcription of the E. coli tufB and recA operons in a cell-free system containing of purified RNA polymerase holoenzyme. The transcription of the tufB operon which is under stringent control, was markedly inhibited by 0.5 mM ppGpp, and the extent of this inhibition was found to be greatly influenced by the Mg2+ and K+ concentrations in the reaction mixture. Maximal inhibition was obtained in the presence of 2 mM Mg2+ and 80-120 mM K+, whereas at higher concentrations of Mg2+ or lower concentrations of K+, practically no inhibition was observed. In contrast, transcription of the recA operon which is not subject to stringent control, was little affected by ppGpp at any of Mg2+ and K+ concentrations tested. The nucleotide inhibited initiation of transcription of tufB, while the rate of RNA chain elongation was not greatly inhibited in the presence of ppGpp.