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Updated: Aug 16, 2026

The Multifaceted Benefits of Protein Co-expression in Escherichia coli
Published on: February 5, 2015
Complex transcriptional control links NikABCDE-dependent nickel transport with hydrogenase expression in Escherichia
Jessica L Rowe1, G Lucas Starnes, Peter T Chivers
1Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, Saint Louis, Missouri 63110, USA.
Abstract:
Escherichia coli requires nickel under anaerobic growth conditions for the synthesis of catalytically active NiFe hydrogenases. Transcription of the NikABCDE nickel transporter, which is required for NiFe hydrogenase synthesis, was previously shown to be upregulated by FNR (fumarate-nit rate regulator) in the absence of oxygen and repressed by the NikR repressor in the presence of high extracellular nickel levels. We present here a detailed analysis of nikABCDE transcriptional regulation and show that it closely correlates with hydrogenase expression levels. We identify a nitrate-dependent mechanism for nikABCDE repression that is linked to the NarLX two-component system. NikR is functional under all nickel conditions tested, but its activity is modulated by the total nickel concentration present as well as by one or more components of the hydrogenase assembly pathway. Unexpectedly, NikR function is independent of NikABCDE function, suggesting that NikABCDE is a hydrogenase-specific nickel transporter, consistent with its original identification as a hydrogenase (hyd) mutant. Further, the results suggest that the hydrogenase assembly pathway is sequestered within the cell. A second nickel import pathway in E. coli is implicated in NikR function.
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