Affiliation:
1. Departments of Microbiology
2. Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
Abstract
ABSTRACT
Recently, Nie and coworkers (L. Nie, Y. Ren, A. Janakiraman, S. Smith, and H. Schulz, Biochemistry 47:9618-9626, 2008) reported a new
Escherichia coli
thioesterase encoded by the
ybaW
gene that cleaves the thioester bonds of inhibitory acyl-coenzyme A (CoA) by-products generated during β-oxidation of certain unsaturated fatty acids. These authors suggested that
ybaW
expression might be regulated by FadR, the repressor of the
fad
(fatty acid degradation) regulon. We report mapping of the
ybaW
promoter and show that
ybaW
transcription responded to FadR in vivo. Moreover, purified FadR bound to a DNA sequence similar to the canonical FadR binding site located upstream of the
ybaW
coding sequence and was released from the promoter upon the addition of long-chain acyl-CoA thioesters. We therefore propose the designation
fadM
in place of
ybaW
. Although FadR regulation of
fadM
expression had the pattern typical of
fad
regulon genes, its modulation by the cyclic AMP (cAMP) receptor protein-cAMP complex (CRP-cAMP) global regulator was the opposite of that normally observed. CRP-cAMP generally acts as an activator of
fad
gene expression, consistent with the low status of fatty acids as carbon sources. However, glucose growth stimulated
fadM
expression relative to acetate growth, as did inactivation of CRP-cAMP, indicating that the complex acts as a negative regulator of this gene. The stimulation of
fadM
expression seen upon deletion of the gene encoding adenylate cyclase (Δ
cya
) was reversed by supplementation of the growth medium with cAMP. Nie and coworkers also reported that growth on a conjugated linoleic acid isomer yields much higher levels of FadM thioesterase activity than does growth on oleic acid. In contrast, we found that the conjugated linoleic acid isomer was only a weak inducer of
fadM
expression. Although the gene is not essential for growth, the high basal level of
fadM
expression under diverse growth conditions suggests that the encoded thioesterase has functions in addition to β-oxidation.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
42 articles.
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