Journal of Bacteriology, May 2001, p. 2842-2851, Vol. 183, No. 9
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.9.2842-2851.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
54-Dependent Po
Promoter
Department of Cell and Molecular Biology, Umeå University, S-901 87 Umeå, Sweden
Received 23 October 2000/Accepted 20 February 2001
Transcription from the Pseudomonas CF600-derived
54-dependent promoter Po is controlled by the
aromatic-responsive activator DmpR. Here we examine the mechanism(s) by
which integration host factor (IHF) stimulates DmpR-activated
transcriptional output of the Po promoter both in vivo and in vitro. In
vivo, the Po promoter exhibits characteristics that typify many
54-dependent promoters, namely, a phasing-dependent
tolerance with respect to the distance from the regulator binding sites
to the distally located RNA polymerase binding site, and a strong
dependence on IHF for optimal promoter output. IHF is shown to affect
transcription via structural repercussions mediated through binding to
a single DNA signature located between the regulator and RNA polymerase binding sites. In vitro, using DNA templates that lack the regulator binding sites and thus bypass a role of IHF in facilitating physical interaction between the regulator and the transcriptional apparatus, IHF still mediates a DNA binding-dependent stimulation of Po
transcription. This stimulatory effect is shown to be independent of
previously described mechanisms for the effects of IHF at
54 promoters such as aiding binding of the regulator or
recruitment of
54-RNA polymerase via UP element-like
DNA. The effect of IHF could be traced to promotion and/or
stabilization of open complexes within the nucleoprotein complex that
may involve an A+T-rich region of the IHF binding site and
promoter-upstream DNA. Mechanistic implications are discussed in the
context of a model in which IHF binding results in transduction of DNA
instability from an A+T-rich region to the melt region of the promoter.
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