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J. Bacteriol., Apr 1997, 2221-2227, Vol 179, No. 7
SA Chugani, MR Parsek, CD Hershberger, K Murakami, A Ishihama and AM Chakrabarty
The soil bacterium Pseudomonas putida is capable of degrading many aromatic
compounds, including benzoate, through catechol as an intermediate. The
catabolism of catechol is mediated by the catBCA operon, whose induction
requires the pathway intermediate cis,cis- muconate as an inducer and the
regulatory protein, CatR. CatR also regulates the plasmid-borne pheBA
operon of P. putida PaW85, which is involved in phenol catabolism. We have
used an in vitro transcription system to study the roles of CatR,
cis,cis-muconate, Escherichia coli RNA polymerase, and promoter sequences
in expression of the cat and phe operons. The assay confirmed the
requirement of both CatR and cis,cis- muconate for transcript formation. We
also examined the in vitro transcription of three site-directed mutants of
the catBCA promoter; the results obtained compared favorably with previous
in vivo data. The requirement of the alpha subunit of RNA polymerase for
expression of the catBCA and the pheBA transcripts was also examined. The
C-terminal region of the alpha subunit of RNA polymerase has been
implicated in direct protein-protein contact with transcriptional
regulatory proteins and/or direct contact with the DNA. We show that the
carboxyl terminus of the alpha subunit is required for the expression of
the catBCA and the pheBA operons because RNA polymerases with truncated
alpha subunits were deficient in activation. Further experiments
demonstrated the arginine at position 265 and the asparagine at position
268 of the alpha subunit as possible amino acids involved in activation. On
the basis of these and previous results, we propose a model to explain the
interaction of the different regulatory components leading to CatR-
dependent activation of the catBCA operon.
Copyright © 1997, American Society for Microbiology
Activation of the catBCA promoter: probing the interaction of CatR and RNA polymerase through in vitro transcription
Department of Microbiology and Immunology, University of Illinois College of Medicine, Chicago 60612, USA.
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