Journal of Bacteriology, January 2001, p. 270-279, Vol. 183, No. 1
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183-1.270-279.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


Swiss Federal Institute for Environmental Science and Technology and Swiss Federal Institute of Technology, CH-8600 Dübendorf,1 and Institute of Biotechnology, Swiss Federal Institute of Technology, CH-8093 Zürich,2 Switzerland
Received 3 August 2000/Accepted 6 October 2000
Pseudomonas azelaica HBP1 degrades the toxic substance
2-hydroxybiphenyl (2-HBP) by means of three enzymes that are encoded by
structural genes hbpC, hbpA, and
hbpD. These three genes form a small noncontiguous cluster.
Their expression is activated by the product of regulatory gene
hbpR, which is located directly upstream of the
hbpCAD genes. The HbpR protein is a transcription activator
and belongs to the so-called XylR/DmpR subclass within the NtrC family
of transcriptional activators. Transcriptional fusions between the
different hbp intergenic regions and the luxAB genes of Vibrio harveyi in P. azelaica and in
Escherichia coli revealed the existence of two
HbpR-regulated promoters; one is located in front of hbpC,
and the other one is located in front of hbpD. Northern
analysis confirmed that the hbpC and hbpA genes are cotranscribed, whereas the hbpD gene is transcribed
separately. No transcripts comprising the entire hbpCAD
cluster were detected, indicating that transcription from
PhbpC is terminated after the hbpA
gene. E. coli mutant strains lacking the structural genes
for the RNA polymerase
54 subunit or for the integration
host factor failed to express bioluminescence from
PhbpC- and PhbpD-luxAB fusions when a functional hbpR gene was provided in
trans. This pointed to the active role of
54
and integration host factor in transcriptional activation from these
promoters. Primer extension analysis revealed that both PhbpC and PhbpD contain
the typical motifs at position
24 (GG) and
12 (GC) found in
54-dependent promoters. Analysis of changes in the
synthesis of the hbp mRNAs, in activities of the 2-HBP
pathway enzymes, and in concentrations of 2-HBP intermediates during
the first 4 h after induction of continuously grown P. azelaica cells with 2-HBP demonstrated that the specific
transcriptional organization of the hbp genes ensured
smooth pathway expression.
Present address: Department of Microbiology, Wageningen
Agricultural University, Wageningen, The Netherlands.
Present address: Institute for Plant Science, Swiss Federal
Institute of Technology, CH-8092 Zürich, Switzerland.
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