In Vivo Demonstration of FNR Dimers in Response to Lower O ₂ Availability

Escherichia coli FNR is an O(2)-sensing transcription factor. In vitro studies indicate that anaerobic iron-sulfur cluster acquisition promotes FNR dimerization. Here, two-hybrid assays show that iron-sulfur cluster-dependent FNR dimers are formed in vivo in response to lower O(2) availability, consistent with the current model of FNR activation.