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J. Bacteriol., Jan 1996, 266-272, Vol 178, No. 1
D Parke
Previous work demonstrated that catabolism of the phenolic compounds p-
hydroxybenzoate and protocatechuate via the beta-ketoadipate pathway in
Agrobacterium tumefaciens is mediated by a regulatory gene, pcaQ, that acts
in trans to elicit expression of many of the enzymes encoded by the pca
genes. There was evidence that five pca structural genes are organized in a
polycistronic operon transcribed in the order pcaDCHGB. The pcaQ gene is
upstream of this operon. The activator encoded by pcaQ was novel in having
the metabolite beta-carboxy-cis,cis-muconate as a coinducer. This
communication reports the nucleotide sequence of pcaQ and identifies its
deduced polypeptide product as a member of the LysR family of regulatory
molecules. PcaQ has a calculated molecular weight of 33,546, which is
consistent with the size of LysR relatives. Like many other LysR members,
PcaQ serves as an activator at the level of transcription, it has a
conserved amino-terminal domain, and its gene is transcribed divergently
from the operon that it regulates and is subject to negative
autoregulation. Studies of coinducer specificity identified an unstable
pathway metabolite, gamma-carboxymuconolactone, as a second coinducer.
Analysis of expression from a pcaD::lacZ promoter probe plasmid revealed
that PcaQ and the coinducer exert their effect on a 133-nucleotide region
upstream of pcaD. The nucleotide sequence of this region in a mutant strain
constitutive for enzymes encoded by the pcaDCHGB operon identified
nucleotides likely to be involved in the pcaDCHGB promoter and
substantiated the inclusion of five pca structural genes in the operon.
Copyright © 1996, American Society for Microbiology
Characterization of PcaQ, a LysR-type transcriptional activator required for catabolism of phenolic compounds, from Agrobacterium tumefaciens
Department of Biology, Yale University, New Haven, Connecticut 06520- 8103, USA.
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