Iron-sulfur cluster assembly enzyme, also known as ISCU, is a member of the nifU family. Iron-sulfur (Fe-S) clusters are necessary for several mitochondrial enzymes and other subcellular compartment proteins. It is interact with ISCS, a cysteine desulfurase, to sequester inorganic sulfur for Fe-S cluster assembly. ISCU-ISCS protein complex localizes in both mitochondria and cytosol, implying that Fe-S cluster assembly takes place in multiple subcellular compartments in mammalian cells