Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 98, Issue 26, Pages 14895-14900Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.251550898
Keywords
cofactor synthesis; metalloproteins; MarA; transcriptional regulator; EPR
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Funding
- NIGMS NIH HHS [T32 GM008349, R01 GM045844, GM-45844, GM08349] Funding Source: Medline
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IscR (iron-sulfur cluster regulator) is encoded by an ORF located immediately upstream of genes coding for the Escherichia coli Fe-S cluster assembly proteins, IscS, IscU, and IscA. IscR shares amino acid similarity with MarA, a member of the MarA/SoxS/Rob family of transcription factors. In this study, we found that IscR functions as a repressor of the iscRSUA operon, because strains deleted for iscR have increased expression of this operon. In addition, in vitro transcription reactions established a direct role for IscR in repression of the iscR promoter. Analysis of IscR by electron paramagnetic resonance showed that the anaerobically isolated protein contains a [2Fe-2S](1+) cluster. The Fe-S cluster appears to be important for IscR function, because repression of iscR expression is significantly reduced in strains containing null mutations of the Fe-S cluster assembly genes iscS or hscA. The finding that IscR activity is decreased in strain backgrounds in which Fe-S cluster assembly is impaired suggests that this protein may be part of a novel autoregulatory mechanism that senses the Fe-S cluster assembly status of cells.
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