Fnr, a Global Transcriptional Regulator of Escherichia coli, Activates the Vitreoscilla Hemoglobin (VHb) Promoter and Intracellular VHb Expression Increases Cytochrome d Promoter Activity

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Abstract
The oxygen‐regulated promoter (Pvhb) of the Vitreoscilla hemoglobin gene has been applied to direct high‐level expression of several cloned proteins, including Vitreoscilla hemoglobin (VHb), which improves productivity of many aerobic processes. In an effort to gain a better understanding of the regulation of Pvhb, and to guide further optimization of this technology, we investigated whether the Escherichia coli global regulatory molecules Fnr and the Arc system (ArcA and ArcB), which control the expression of various genes under either aerobic or anaerobic conditions, also regulate Pvhb activity in E. coli. The activity of Pvhb and the expression of VHb in E. coli were activated by Fnr, but were relatively unaffected by the Arc system under microaerobic conditions (DO less than 2% air saturation). We also examined the possibility of VHb affecting cytochrome d promoter activity during microaerobiosis. The presence of VHb increased the activity of β‐galactosidase from a cytochrome d promoter‐lacZ fusion by 1.5‐fold. This indicates that VHb affects oxygen‐regulated transcription of E. coli genes and may contribute to the modified physiology observed in VHb‐expressing E. coli.