Hierarchy of the strength of Escherichia coli stringent control signals.

The quantitative effect of ppGpp, the effector of stringent control, on various Escherichia coli promoters was measured in an in vitro mixed transcription system. This allowed us to determine, among these promoters, the hierarchy of promoters according to their ppGpp susceptibility. The strength of the stringent control signal, however, was found to be altered when the test promoters were transcribed by ppGpp-insensitive RNA polymerases from relaxed mutants of E. coli, which carry substitutions in the beta subunit gene (rpoB). Thus, it was concluded that the activity of the stringent control signal depends on the nature of the RNA polymerase as well as that of the promoter.