NDLI: ArcA and AppY Antagonize IscR Repression of Hydrogenase-1 Expression under Anaerobic Conditions, Revealing a Novel Mode of O2 Regulation of Gene Expression in Escherichia coli

Content Provider	PubMed Central
Author	Nesbit, A. D. Fleischhacker, A. S. Teter, S. J. Kiley, P. J.
Copyright Year	2012
Abstract	Transcription of the Escherichia coli hydrogenase-1 operon (hyaABCDEF) is increased by the transcription factors ArcA and AppY under anaerobic growth conditions. However, IscR, which represses transcription of the hyaA promoter (P hyaA ) under aerobic conditions, was not known to repress transcription of this promoter under anaerobic conditions. Here, we report that ArcA and AppY increase P hyaA expression under anaerobic conditions by antagonizing IscR binding at P hyaA , since IscR repression is observed when either ArcA or AppY is eliminated. The ability of ArcA and AppY to act as antirepressors of IscR repression of P hyaA depended on IscR levels, suggesting that IscR competes with ArcA and/or AppY for binding. In support of this competition model, electrophoretic mobility shift assays and DNase I footprinting showed that the ArcA and IscR binding sites overlap and that binding of ArcA and IscR is mutually exclusive. Unexpectedly, IscR with a C92A mutation (IscR-C92A), which mimics the clusterless form of the protein that is present predominantly under aerobic conditions, was a better repressor under anaerobic conditions of both P hyaA and a constitutive promoter containing the IscR binding site from P hyaA than wild-type IscR, which is predominantly in the [2Fe-2S] form under anaerobic conditions. This observation could not be explained by differences in DNA binding affinities or IscR levels, so we conclude that [2Fe-2S]-IscR is a weaker repressor of P hyaA than clusterless IscR. In sum, a combination of ArcA and AppY antirepression of IscR function, lower levels of IscR, and weak repression by [2Fe-2S]-IscR leads to increased P hyaA expression under anaerobic conditions.
Related Links	http://dx.doi.org/10.1128/jb.01757-12
Ending Page	6899
Page Count	8
Starting Page	6892
File Format	PDF
ISSN	00219193
e-ISSN	10985530
Journal	Journal of Bacteriology
Issue Number	24
Volume Number	194
Language	English
Publisher	American Society for Microbiology
Publisher Date	2012-12-15
Access Restriction	Open
Rights Holder	American Society for Microbiology
Subject Keyword	Molecular Biology Microbiology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Molecular Biology Microbiology

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