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Updated: Jun 26, 2026

Determination of the Optimal Chromosomal Location(s) for a DNA Element in Escherichia coli Using a Novel Transposon-mediated Approach
Published on: September 11, 2017
Allosteric control of Escherichia coli rRNA promoter complexes by DksA
Steven T Rutherford1, Courtney L Villers, Jeong-Hyun Lee
1Department of Bacteriology, University of Wisconsin at Madison, Madison, Wisconsin 53706, USA.
Abstract:
The Escherichia coli DksA protein inserts into the RNA polymerase (RNAP) secondary channel, modifying the transcription initiation complex so that promoters with specific kinetic characteristics are regulated by changes in the concentrations of ppGpp and NTPs. We used footprinting assays to determine the specific kinetic intermediate, RP(I), on which DksA acts. Genetic approaches identified substitutions in the RNAP switch regions, bridge helix, and trigger loop that mimicked, reduced, or enhanced DksA function on rRNA promoters. Our results indicate that DksA binding in the secondary channel of RP(I) disrupts interactions with promoter DNA at least 25 A away, between positions -6 and +6 (the transcription start site is +1). We propose a working model in which the trigger loop and bridge helix transmit effects of DksA to the switch region(s), allosterically affecting switch residues that control clamp opening/closing and/or that interact directly with promoter DNA. DksA thus inhibits the transition to RP(I). Our results illustrate in mechanistic terms how transcription factors can regulate initiation promoter-specifically without interacting directly with DNA.
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