Component of the cytosolic iron-sulfur (Fe/S) protein assembly (CIA) machinery. Required for maturation of extramitochondrial Fe-S proteins. The nubp1-nubp2 heterotetramer forms a Fe-S scaffold complex, mediating the de novo assembly of an Fe-S cluster and its transfer to target apoproteins. Binds 4 [4Fe-4S] clusters per heterotetramer. Contains two stable clusters in the N-termini of nubp1 and two labile, bridging clusters between subunits of the nubp1-nubp2 heterotetramer. Heterotetramer of 2 nubp1 and 2 nubp2 chains. Belongs to the Mrp/NBP35 ATP-binding proteins family. NUBP2/CFD1 subfamily.