Escherichia coli rnpB promoter mutants altered in stringent response.

The promoter of the rnpB gene (encoding the RNA component of Escherichia coli RNase P) shares a consensus discriminator sequence, located between the -10 hexamer sequence and the transcription start site, with other promoters whose activities are repressed upon stringent condition. Under stringent conditions induced by seryl-tRNA starvation the transcription of the rnpB gene was repressed in wild type E. coli but not in a relaxed strain carrying a relA- mutation. Site-directed mutagenesis was carried out to examine sequences of the rnpB promoter necessary for stringent control. The results indicate that the discriminator region is responsible for the transcription repression of the rnpB gene during the stringent response and that both the content and position of GC pairs in the region determine the strength of negative stringent signals.