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. Author manuscript; available in PMC: 2011 Apr 9.
Published in final edited form as: J Mol Biol. 2010 Feb 12;397(4):893–905. doi: 10.1016/j.jmb.2010.02.015

Fig 1.

Fig 1

A representation of the FNR system in E. coli. FNR regulates the shift between aerobic and anaerobic growth. Dimeric 4Fe-FNR adapts the cell to oxygen-limiting conditions. Aerobically, oxygen inactivates FNR, but the cell continues to produce and reactivate it. This results in constant cycling of FNR between its three states—apoFNR, 4Fe-FNR, and 2Fe-FNR. Aerobic cycling is tuned so that the inactive apoFNR predominates. Under anaerobic conditions, the absence of oxygen results in rapid buildup of 4Fe-FNR. The 4Fe-FNR form dimerizes to produce an active transcription factor.