Iron-sulfur cluster scaffold protein which can assemble [4Fe- 4S] clusters and deliver them to target proteins. {ECO:0000269|PubMed:12886008, ECO:0000269|PubMed:27818104, ECO:0000269|PubMed:28906594}. This is the function of NFU1 (NFU1 iron-sulfur cluster scaffold, ENSG00000169599).