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Journal of Bacteriology, June 1999, p. 3402-3408, Vol. 181, No. 11
TB Center,
Received 12 March 1998/Accepted 30 March 1999
Exochelin is the primary extracellular siderophore of
Mycobacterium smegmatis, and the iron-regulated
fxbA gene encodes a putative formyltransferase, an
essential enzyme in the exochelin biosynthetic pathway (E. H. Fiss, Y. Yu, and W. R. Jacobs, Jr., Mol. Microbiol. 14:557-569,
1994). We investigated the regulation of fxbA by the
mycobacterial IdeR, a homolog of the Corynebacterium diphtheriae iron regulator DtxR (M. P. Schmitt, M. Predich,
L. Doukhan, I. Smith, and R. K. Holmes, Infect. Immun.
63:4284-4289, 1995). Gel mobility shift experiments showed that IdeR
binds to the fxbA regulatory region in the presence of
divalent metals. DNase I footprinting assays indicated that IdeR
binding protects a 28-bp region containing a palindromic sequence of
the fxbA promoter that was identified in primer extension
assays. fxbA regulation was measured in M. smegmatis wild-type and ideR mutant strains containing fxbA promoter-lacZ fusions. These
experiments confirmed that fxbA expression is negatively
regulated by iron and showed that inactivation of ideR
results in iron-independent expression of fxbA. However,
the levels of its expression in the ideR mutant were
approximately 50% lower than those in the wild-type strain under iron
limitation, indicating an undefined positive role of IdeR in the
regulation of fxbA.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Transcriptional Control of the Iron-Responsive
fxbA Gene by the Mycobacterial Regulator
IdeR
*
Corresponding author. Mailing address: TB Center,
Public Health Research Institute, 455 First Ave., New York, NY 10016. Phone: (212) 578-0867. Fax: (212) 578-0804. E-mail:
smitty{at}phri.nyu.edu.
Publication no. 64 from the TB Center, Public Health Research Institute.
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