EKR is a short, 33 residue, domain found in bacterial and some lower eukaryotic species which lies between a POR (pyruvate ferredoxin/flavodoxin oxidoreductase) Pfam:PF01558 and the 4Fe-4S binding domain Fer4 Pfam:PF00037. It contains a characteristic EKR sequence motif. The exact function of this domain is not known.