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J. Bacteriol., Aug 1995, 4427-4436, Vol 177, No. 15
AK Hovey and DW Frank
ExsA has been implicated as a central regulator of exoenzyme S production
by Pseudomonas aeruginosa. In this study, the DNA-binding and
transcriptional activation properties of ExsA were investigated. ExsA was
produced and purified as a fusion protein, MALA3A2, which was shown to bind
specifically to promoter regions that regulated transcription of the
exoenzyme S trans-regulatory locus (pC) and a locus located directly
downstream of exsA (pD). Previously, MALA3A2 was shown to bind the exoS 5'
PstI-NsiI region, which contained two independent but coordinately
regulated (ExsA-mediated) promoters, pS' (now termed pORF1) and pS. DNase I
footprint analysis of the promoter regions bound by ExsA revealed a common
protected consensus sequence of TXAAAAXA. The consensus sequence was
located -51 to -52 bp upstream of the transcriptional start sites for pD,
pS, and pORF1. Promoter fusion, DNA-binding, and mutagenesis analysis
indicated that the consensus sequence was important for transcriptional
activation. Each ExsA- controlled promoter region contained at least two
consensus sites in close proximity, similar to the arrangement of
half-sites seen in AraC- controlled (Escherichia coli) or VirF-controlled
(Yersinia enterocolitica) promoters. However, the results of this study
suggested that only one consensus site was required in the exoenzyme S (pS)
or ORF1 promoter (pORF1) to initiate transcription. These data suggest that
members of the exoenzyme S regulon can be defined as possessing an ExsA
consensus element which maps at bp -51 or -52 relative to the
transcriptional start site.
Copyright © 1995, American Society for Microbiology
Analyses of the DNA-binding and transcriptional activation properties of ExsA, the transcriptional activator of the Pseudomonas aeruginosa exoenzyme S regulon
Department of Microbiology, Medical College of Wisconsin, Milwaukee 53226, USA.
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