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Transcription activation parameters at ara pBAD

X Zhang1, T Reeder, R Schleif

  • 1Department of Biology, Johns Hopkins University, Baltimore, MD 21218, USA.

Journal of Molecular Biology
|April 26, 1996
PubMed
Summary

Researchers used DNA migration assays to study RNA polymerase open complex formation at bacterial promoters. This method accurately quantifies open complexes, revealing tight binding of AraC protein to the pBAD promoter.

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Area of Science:

  • Molecular Biology
  • Biochemistry
  • Microbiology

Background:

  • Bacterial gene regulation involves RNA polymerase binding to promoter DNA to form open complexes.
  • Proteins like AraC and cyclic AMP receptor protein (CRP) modulate this binding at specific promoters.
  • Understanding open complex formation is crucial for deciphering gene expression control.

Purpose of the Study:

  • To validate the DNA migration retardation assay for detecting and quantifying RNA polymerase-DNA open complexes.
  • To investigate open complex formation at the Escherichia coli araBAD promoter (pBAD) activated by AraC protein.
  • To analyze open complex formation at the galKTE promoter (P1) activated by CRP.

Main Methods:

  • DNA migration retardation assay to detect and quantify open complexes.
  • Characterization of open complex properties including heparin resistance, lifetime, and DNaseI/exonuclease III/permanganate footprinting.
  • Kinetic analysis of binding using dissociation constant (Kd) and rate constant (k2).

Main Results:

  • The DNA migration retardation assay accurately reflects open complex properties in solution and in gels.
  • Consistent results were observed for both ara and gal promoters, validating the assay's utility.
  • Kinetic parameters for the pBAD promoter were determined as Kd = 0.3 nM and K2 = 1 minute(-1).

Conclusions:

  • The DNA migration retardation assay is a reliable method for studying RNA polymerase-promoter interactions.
  • The unusually tight binding of RNA polymerase to the pBAD promoter in the presence of AraC suggests a strong interaction between AraC and the polymerase.
  • This study provides quantitative insights into transcriptional activation mechanisms in bacteria.

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