RNA-POLYMERASE MUTANTS THAT DESTABILIZE RNA POLYMERASE-PROMOTER COMPLEXES ALTER NTP-SENSING BY RRN P1 PROMOTERS

Mutations in Escherichia coli rpoB or rpoC, selected for the ability t o confer prototrophy on relA spoT strains, were found to affect transc ription from rrn P1 promoters. Two mutant strains (beta RH454 and beta ' Delta 215-220) reduced transcription of rrn P1 core promoter-lacZ fu sions but hot of control promoter-lacZ fusions. Purified mutant RNAPs formed complexes with rrn P1 promoters that were much less stable than those formed by wild-type RNAP and required high concentrations of th e initiating NTP for efficient rrn P1 transcription. The instability o f the rrn P1 core promoter complexes with the mutant RNAPs and their a ltered regulatory properties support a recently proposed model for the control of rRNA transcription by changing concentrations of the initi ating NTPs. We further suggest that destabilization of promoter comple xes by the mutant RNAPs mimics effects of ppGpp, decreasing or increas ing transcription depending on the kinetic properties of the specific promoter. (C) 1998 Academic Press Limited.