Transcription regulator involved in mid-term, stationary-phase viability under nitrogen starvation. Might control expression of the salvage pathways or in some other way repress the recycling of nucleobases to nucleic acids and enhance their use as general nitrogen sources during nitrogen-limited growth. Binds 1 [4Fe-4S] cluster per subunit. Homodimer. In the stationary phase, aerobic expression is positively autoregulated and significantly dependent on RpoS and Lrp. Its transcription is directly or indirectly repressed by FNR. Its activity might be modulated by a sensory iron-sulfur cluster, by reversible dithiol-disulfide formation, or by both mechanisms. It is not an oxygen-responsive regulator.