Member of the two-component regulatory system DevR/DevS (DosR/DosS) involved in onset of the dormancy response (PubMed:12953092). Regulates an approximately 48-member regulon (PubMed:12953092, PubMed:11416222, PubMed:15033981, PubMed:18400743). Required for full induction of the DevR (DosR) regulon; acts later than DosT to positively regulate expression of the DevR regulon during adaptation to anaerobiosis (PubMed:19487478). Characterized as an oxygen sensor; O(2) acts as a switch, with O(2)-bound Fe(2+) protein inactive in autophosphorylation (PubMed:17371046, PubMed:17600145, PubMed:18975917, PubMed:19463006, PubMed:28977726). Has also been suggested to act as a redox sensor, or perhaps as a dual oxygen/redox sensor (PubMed:17609369). Autophosphorylates under anaerobic but not aerobic conditions, binding of NO or CO does not dramatically change the level of autophosphorylation of Fe(2+) protein, binding of O(2) inactivates kinase activity (PubMed:17600145, PubMed:18975917, PubMed:27235395). Binds O(2), NO, CO (PubMed:17371046, PubMed:17609369, PubMed:17600145, PubMed:18975917, PubMed:27235395). It is probably reduced by flavin nucleotides such as FMN and FAD (PubMed:19276084). May be the primary sensor for CO (PubMed:18400743). Donates a phosphate group to transcriptional regulator DevR (DosR) (PubMed:15033981, PubMed:15073296, PubMed:28977726).