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J. Bacteriol., 08 1996, 4515-4521, Vol 178, No. 15
S Becker, G Holighaus, T Gabrielczyk and G Unden
With an oxystat, changes in the pattern of expression of FNR-dependent
genes from Escherichia coli were studied as a function of the O2 tension
(pO2) in the medium. Expression of all four tested genes was decreased by
increasing O2. However, the pO2 values that gave rise to half-maximal
repression (pO(0.5)) were dependent on the particular promoter and varied
between 1 and 5 millibars (1 bar = 10(5) Pa). The pO(0.5) value for the
ArcA-regulated succinate dehydrogenase genes was in the same range (pO(0.5)
= 4.6 millibars). At these pO2 values, the cytoplasm can be calculated to
be well supplied with O2 by diffusion. Therefore, intracellular O2 could
provide the signal to FNR, suggesting that there is no need for a signal
transfer chain. Genetic inactivation of the enzymes and coenzymes of
aerobic respiration had no or limited effects on the pO(0.5) of
FNR-regulated genes. Thus, neither the components of aerobic respiration
nor their redox state are the primary sites for O2 sensing, supporting the
significance of intracellular O2. Non-redox-active, structural O2 analogs
like CO, CN-, and N3-, could not mimic the effect of O2 on FNR-regulated
genes under anaerobic conditions and did not decrease the inhibitory effect
of O2 under aerobic conditions.
Copyright © 1996, American Society for Microbiology
O2 as the regulatory signal for FNR-dependent gene regulation in Escherichia coli
Institut fur Mikrobiologie und Weinforschung, Johannes Gutenberg- Universitat Mainz, Germany.
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