Identification and characterization of two divergently transcribed iron regulated genes in Mycobacterium tuberculosis.

Low iron availability in the host induces the expression of iron acquisition systems and virulence genes in many pathogens. IdeR is a mycobacterial iron dependent regulator that controls the iron starvation and oxidative stress responses in Mycobacterium smegmatis. It is important to determine the role of IdeR and its regulon in M. tuberculosis, as identification of iron regulated genes can aid in the design of new drugs and generation of attenuated strains. A potential IdeR binding site was found in the M. tuberculosis genome flanked by two divergently oriented open reading frames, irg1 and irg2. The aim of this study was to determine whether irg1 and irg2 were iron and IdeR regulated genes. Interaction of IdeR with the putative binding sequence was examined by gel shift and footprinting assays. Transcriptional fusions of irg1 and irg2 to IacZ were used to study the effect of iron levels on the expression of these genes. IdeR binds to the predicted binding site, which overlaps with the irg1 promoter. irg1 and irg2 expression was decreased by iron in M. tuberculosis and in wild type M. smegmatis, but not in a M. smegmatis ideR mutant. Two M. tuberculosis iron/IdeR regulated genes were identified. irg1 is predicted to be the M. tuberculosis hisE gene, which is involved in histidine biosynthesis. It is directly upstream of the M. tuberculosis hisG. irg2 encodes a putative membrane protein that is a member of the PPE family.