Recent Articles

Gold B, Rodriguez GM, Marras SA, Pentecost M, Smith I.
The Mycobacterium tuberculosis IdeR is a dual functional regulator that controls transcription of genes involved in iron acquisition, iron storage and survivalin macrophages.
Mol Microbiol 2001 Nov;42(3):851-65
PMID: 11722747

In this work, we characterize genes in Mycobacterium tuberculosis that are
regulated by IdeR (iron-dependent regulator), an iron-responsive DNA-binding
protein of the DtxR family that has been shown to regulate iron acquisition in
Mycobacterium smegmatis. To identify some of the genes that constitute the IdeR
regulon, we searched the M. tuberculosis genome for promoter regions containing
the consensus IdeR/DxR binding sequence. Genes preceded by IdeR boxes included a
set encoding proteins necessary for iron acquisition, such as the biosynthesis
of siderophores (mbtA, mbtB, mbtI), aromatic amino acids (pheA, hisE, hisB-like)
and others annotated to be involved in the synthesis of iron-storage proteins
(bfrA, bfrB). Some putative IdeR-regulated genes identified in this search
encoded proteins predicted to be engaged in the biosynthesis of
lipopolysaccharide (LPS)-like molecules (rv3402c), lipids (acpP) and
peptidoglycan (murB). We analysed four promoter regions containing putative IdeR
boxes, mbtA-mbtB, mbI, rv3402c and bfrA-bfd, for interaction with IdeR and for
iron-dependent expression. Gel retardation experiments and DNase footprinting
analyses with purified IdeR showed that IdeR binds to these IdeR boxes in vitro.
Analysis of the promoters by primer extension indicated that the IdeR boxes are
located near the -10 position of each promoter, suggesting that IdeR acts as a
transcriptional repressor by blocking RNA polymerase binding. Using quantitative
reverse transcriptase-polymerase chain reaction (RT-PCR) coupled to molecular
beacons, we showed that mRNA levels of mbtA, mbtB, mbtI, rv3402c and bfd are
induced 14- to 49-fold in cultures of M. tuberculosis starved for iron, whereas
mRNA levels of bfrA decreased about threefold. We present evidence that IdeR not
only acts as a transcriptional repressor but also functions as an activator of
bfrA. Three of the IdeR- and iron-repressed genes, mbtB, mbtI and rv3402c, were
induced during M. tuberculosis infection of human THP-1 macrophages.