This domain is found at the N terminus of NifU and NifU related proteins, and in the human Nfu protein. Both of these proteins are thought to be involved in the the assembly of iron-sulphur clusters [1][2].

1: Subcellular compartmentalization of human Nfu, an iron-sulfur cluster scaffold protein, and its ability to assemble a [4Fe-4S] cluster. Tong WH, Jameson GN, Huynh BH, Rouault TA; Proc Natl Acad Sci U S A. 2003;100:9762-9767. PMID:12886008

2: Iron-sulfur cluster assembly: NifU-directed activation of the nitrogenase Fe protein. Dos Santos PC, Smith AD, Frazzon J, Cash VL, Johnson MK, Dean DR; J Biol Chem. 2004;279:19705-19711. PMID:14993221