Transcriptional control of the iron-responsive fxbA gene by the mycobacterial regulator IdeR

• Published in: Journal of bacteriology Vol. 181; no. 11; pp. 3402 - 3408
• Main Authors: Dussurget, O, Timm, J, Gomez, M, Gold, B, Yu, S, Sabol, S Z, Holmes, R K, Jacobs, Jr, W R, Smith, I
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 01.06.1999
• Subjects: Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Base Sequence; beta-Galactosidase - genetics; beta-Galactosidase - metabolism; Binding Sites; Cations, Divalent - pharmacology; Cells; Corynebacterium diphtheriae; DNA Footprinting; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Enzymes; Gene Expression Regulation, Bacterial - drug effects; Genes; Genes, Bacterial - genetics; Genes, Reporter; Genetics and Molecular Biology; Hydroxymethyl and Formyl Transferases - genetics; Iron - pharmacology; Mutation; Mycobacterium - drug effects; Mycobacterium - enzymology; Mycobacterium - genetics; Mycobacterium smegmatis; Promoter Regions, Genetic - genetics; Protein Binding - drug effects; Repressor Proteins; Response Elements - genetics; RNA, Messenger - analysis; RNA, Messenger - genetics; Sequence Homology, Amino Acid; Transcription, Genetic - drug effects; Transcription, Genetic - genetics
• ISSN: 0021-9193; 1098-5530
• DOI: 10.1128/jb.181.11.3402-3408.1999

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.