Transcriptional control of the iron-responsive fxbA gene by the mycobacterial regulator IdeR.
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.
Dussurget
O
O
TB Center, Public Health Research Institute, New York, New York 10016, USA.
Timm
J
J
Gomez
M
M
Gold
B
B
Yu
S
S
Sabol
S Z
SZ
Holmes
R K
RK
Jacobs
W R
WR
Smith
I
I
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D002413:Cations, Divalent / Q000494:pharmacology; D018983:DNA Footprinting; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D005798:Genes, Bacterial / Q000235:genetics; D017930:Genes, Reporter; D019877:Hydroxymethyl and Formyl Transferases / Q000235:genetics; D007501:Iron / Q000494:pharmacology*; D009154:Mutation; D009161:Mycobacterium / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D012097:Repressor Proteins; D020218:Response Elements / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic / Q000187:drug effects / Q000235:genetics*; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
D001426:Bacterial Proteins; D002413:Cations, Divalent; D004268:DNA-Binding Proteins; C096348:IdeR protein, Mycobacterium tuberculosis; D012333:RNA, Messenger; D012097:Repressor Proteins; D007501:Iron; D019877:Hydroxymethyl and Formyl Transferases; D001616:beta-Galactosidase