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J. Bacteriol., 05 1997, 3171-3180, Vol 179, No. 10
RW Eaton
Pseudomonas putida F1 utilizes p-cymene (p-isopropyltoluene) by an 11- step
pathway through p-cumate (p-isopropylbenzoate) to isobutyrate, pyruvate,
and acetyl coenzyme A. The cym operon, encoding the conversion of p-cymene
to p-cumate, is located just upstream of the cmt operon, which encodes the
further catabolism of p-cumate and is located, in turn, upstream of the tod
(toluene catabolism) operon in P. putida F1. The sequences of an 11,236-bp
DNA segment carrying the cym operon and a 915-bp DNA segment completing the
sequence of the 2,673-bp DNA segment separating the cmt and tod operons
have been determined and are discussed here. The cym operon contains six
genes in the order cymBCAaAbDE. The gene products have been identified both
by functional assays and by comparing deduced amino acid sequences to
published sequences. Thus, cymAa and cymAb encode the two components of
p-cymene monooxygenase, a hydroxylase and a reductase, respectively; cymB
encodes p-cumic alcohol dehydrogenase; cymC encodes p-cumic aldehyde
dehydrogenase; cymD encodes a putative outer membrane protein related to
gene products of other aromatic hydrocarbon catabolic operons, but having
an unknown function in p-cymene catabolism; and cymE encodes an acetyl
coenzyme A synthetase whose role in this pathway is also unknown. Upstream
of the cym operon is a regulatory gene, cymR. By using recombinant bacteria
carrying either the operator-promoter region of the cym operon or the cmt
operon upstream of genes encoding readily assayed enzymes, in the presence
or absence of cymR, it was demonstrated that cymR encodes a repressor which
controls expression of both the cym and cmt operons and is inducible by
p-cumate but not p- cymene. Short (less than 350 bp) homologous DNA
segments that are located upstream of cymR and between the cmt and tod
operons may have been involved in recombination events that led to the
current arrangement of cym, cmt, and tod genes in P. putida F1.
Copyright © 1997, American Society for Microbiology
p-Cymene catabolic pathway in Pseudomonas putida F1: cloning and characterization of DNA encoding conversion of p-cymene to p-cumate
National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Gulf Breeze, Florida 32561, USA. eaton.richard@epamail.epa.gov
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