IscR, an Fe-S cluster-containing transcription factor, represses expression of Escherichia coli genes encoding Fe-S cluster assembly proteins.
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.
Schwartz
C J
CJ
Department of Biomolecular Chemistry, Microbiology Doctoral Training Program, and Institute for Enzyme Research, University of Wisconsin, Madison, WI 53706, USA.
Giel
J L
JL
Patschkowski
T
T
Luther
C
C
Ruzicka
F J
FJ
Beinert
H
H
Kiley
P J
PJ
D000595:Amino Acid Sequence; D004269:DNA, Bacterial; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D005798:Genes, Bacterial; D007506:Iron-Sulfur Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D007506:Iron-Sulfur Proteins; C499695:IscR protein, E coli; D012097:Repressor Proteins; D014157:Transcription Factors