IscR‐dependent gene expression links iron‐sulphur cluster assembly to the control of O 2 ‐regulated genes in Escherichia coli

Abstract

Summary: IscR is an iron‐sulphur (Fe‐S) cluster‐containing transcription factor that represses transcription of the operon containing its own gene and the iscSUA‐hscBA‐fdx genes, whose products are involved in Fe‐S cluster biogenesis. In this study, global transcriptional profiling of Escherichia coli IscR + and IscR – strains grown under aerobic and anaerobic conditions indicated that 40 genes in 20 predicted operons were regulated by IscR. DNase I footprinting and/or in vitro transcription reactions identified seven new promoters under direct IscR control. Among these were genes encoding known or proposed functions in Fe‐S cluster biogenesis ( sufABCDSE , yadR and yhgI ) and Fe‐S cluster‐containing anaerobic respiratory enzymes ( hyaABCDEF , hybOABCDEFG and napFDAGHBC ). The finding that IscR repressed expression of the hyaA , hybO and napF promoters specifically under aerobic growth conditions suggests a new mechanism to explain their upregulation under anaerobic growth conditions. Phylogenetic footprinting of the DNase I protected regions of seven promoters implies that there are at least two different classes of IscR binding sites conserved among many bacteria. The findings presented here indicate a more general role of IscR in the regulation of Fe‐S cluster biogenesis and that IscR contributes to the O 2 regulation of several promoters controlling the expression of anaerobic Fe‐S proteins.