Figure 1.

(A) IderR regulates Mtb siderophore biosynthesis and iron storage. The mbtA-J genes synthesize the siderphore core and the mbtL-K genes synthesize the mbtK-acyl complex. Transcription of the siderphore biosynthesis genes is inhibited under iron-sufficient conditions and synthesis of the iron storage proteins is activated when the IdeR-Fe²⁺ complex binds to the IdeR boxes in the mbt locus and upstream of the bfrA gene. Under iron limiting conditions the IdeR-Fe²⁺ complex does not form and does not bind to the IdeR box in the mbtB locus, allowing HupB to bind to the hupB box upstream of the IdeR box activating transcription of the mbt genes. In the absence of the IdeR-Fe²⁺ complex transcription of the iron storage genes bfrA and bfrB is repressed. Panel (A) is adapted from Sritharan (12). (B) Fe-S biogenesis machinery in Mtb encoded by a single operon (sufR-sufB-sufD-sufC-csd-nifU-sufT). All the genes in the operon, except for sufR, were predicted to be essential by forward genetic screens. This figure is adapted from Willemse (29).