Transcriptional regulation of mycobacterium tuberculosis hupB gene expression

Abstract

The influence of iron levels on the transcription of the hupB gene in Mycobacterium tuberculos is the focus of this study. Studies in our laboratory showed HupB to be co-expressed with the tw siderophores in low-iron organisms. Mycobactin biosynthesis is repressed by the IdeR-Fe2+ complex that binds the IdeR box in the mbtB promoter. Recently, we demonstrated the positiv regulatory effect of HupB on mycobactin biosynthesis by demonstrating its binding to a 10 bp HupB box in the mbtB promoter. Earlier, we observed that HupB, expressed maximally in low-iro media (0.02 μg Fe ml"1; 0.36 μM Fe) was still detectable at 8 μg Fe ml"1 (144 μM Fe) when th siderophores were absent and complete repression was seen only at 12 μg Fe ml"1 (216 μM Fe In this study, we observed elevated levels of hupB transcripts in iron-limited organisms. IdeR, an not FurA, functioned as the iron regulator, by binding to two IdeR boxes in the hupB promoter Interestingly, the 10 bp HupB box, first reported in the mbtB promoter, was identified in the hup promoter. Using DNA footprinting and electrophoretic mobility shift assays, we demonstrated th functionality of the HupB box and the two IdeR boxes. The high hupB transcript levels expresse by the organism and the in vitro protein-DNA interaction studies led us to hypothesize the sequence of events occurring in response to changes in the intracellular iron concentration, emphasizing the roles played by IdeR and HupB in iron homeostasis. © 2014 The Authors.