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Journal of Bacteriology, October 2006, p. 6953-6965, Vol. 188, No. 19
0021-9193/06/$08.00+0 doi:10.1128/JB.00681-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
P Response Regulator: Bacillus amyloliquefaciens FZB45 Phytase Gene Transcription Is Directed by Positive and Negative Interactions with the phyC Promoter
Institut für Biologie, Humboldt Universität Berlin, Chausseestrasse 117, D-10115 Berlin, Germany,1 Unité de Biologie des Bactéries Pathogènes à Gram Positif, CNRS URA 2172, Institut Pasteur, 25 rue du Dr ROUX, 75724 Paris Cedex 15, France2
Received 12 May 2006/ Accepted 17 July 2006
Several Bacillus strains secrete phytase, an enzyme catalyzing
dephosphorylation of myo-inositol hexakisphosphate (phytate).
We identified the phyC (phytase) gene from environmental
Bacillus amyloliquefaciens FZB45 as a member of the phosphate
starvation-inducible PhoPR regulon. In vivo and in vitro assays
revealed that PhoP
P is essential for phyC
transcription. The transcriptional start site was identified downstream
of a
A-like promoter region located 27 bp upstream
of the probable translation ATG start codon. Inspection of the
phyC promoter sequence revealed an unusual structure. The
35 and 10 regions are separated by a window of 21 bp.
A pair of tandemly repeated PhoP TT(T/A/C)ACA binding boxes was located
within and upstream of the 35 consensus promoter region. A
single PhoP box was found within the 10 consensus promoter
region. DNase I footprinting experiments performed with isolated PhoP
confirmed that PhoP
P binds at two sites overlapping with the
phyC 35 and 10 consensus promoter region.
While binding of dimeric PhoP
P at 35 is essential for
activation of the phyC promoter, binding of PhoP
P at
10 suppresses promoter activity. A sixfold enhancement of
phyC gene expression was registered after T:G substitution of
nucleotide 13 (mutant MUT13), which eliminates PhoP binding at
the single PhoP box without impairing the 10 consensus
sequence. Moreover, MUT13 also expressed phyC during
phosphate-replete growth, suggesting that the repressing effect due to
binding of PhoP
P at 10 was abolished. A model is
presented in which transcription initiation of phyC is
positively and negatively affected by the actual concentration of the
PhoP
P response
regulator.
Supplemental material for this article may be found at http://jb.asm.org/.
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