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Journal of Bacteriology, February 2001, p. 873-881, Vol. 183, No. 3
Department of Microbiology and Biotechnology,
University of Ulm, 89069 Ulm, Germany
Received 2 October 2000/Accepted 13 November 2000
Protocatechuate degradation is accomplished in a multistep
inducible catabolic pathway in Acinetobacter sp. strain
ADP1. The induction is brought about by the transcriptional regulator
PcaU in concert with the inducer protocatechuate. PcaU, a member of the
new IclR family of transcriptional regulators, was shown to play a role
in the activation of transcription at the promoter for the structural
pca genes, leaving open the participation of additional
activators. In this work we show that there is no PcaU-independent transcriptional activation at the pca gene promoter. The
minimal inducer concentration leading to an induction response is
10
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.3.873-881.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Effects Exerted by Transcriptional Regulator PcaU
from Acinetobacter sp. Strain ADP1
5 M protocatechuate. The extent of expression of the
pca genes was observed to depend on the nature of the
inducing carbon source, and this is assumed to be caused by different
internal levels of protocatechuate in the cells. The basal level of
expression was shown to be comparatively high and to vary depending on
the noninducing carbon source independent of PcaU. In addition to the
activating function, in vivo results suggest a repressing function for
PcaU at the pca gene promoter in the absence of an elevated
inducer concentration. Expression at the pcaU gene promoter is independent of the growth condition but is subject to strong negative autoregulation. We propose a model in which PcaU exerts a
repressor function both at its own promoter and at the structural gene
promoter and in addition functions as an activator of transcription at
the structural gene promoter at elevated inducer concentration.
*
Corresponding author. Mailing address: Department of
Microbiology and Biotechnology, University of Ulm, 89069 Ulm, Germany. Phone: 49-731-502-2715. Fax: 49-731-502-2719. E-mail:
ulrike.gerischer{at}biologie.uni-ulm.de.
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