Involved in iron homeostasis within the mitochondrion where it is involved in the assembly of iron-sulfur proteins (PubMed:10468587, PubMed:27532773). Together with BOL3, required during the last step of iron-sulfur protein assembly when the iron-sulfur cluster is inserted into the target protein (PubMed:27532773). Required for protecting iron sulfur clusters from oxidative damage (PubMed:27532773). Homodimer; in absence of BOL3, probably bridged by an iron-sulfure cluster (PubMed:27532773). Interacts with BOL3 (PubMed:27532773). Interacts with apo-target proteins, such as ACO1, LYS4, ACO2 and SDH2 (PubMed:27532773). The CxxC motif may bind a [4Fe-4S] cluster. Cells are impaired in growth on synthetic complete medium with acetate as a carbon source due to defects in mitochondrial [4Fe-4S] cluster formation. Present with 11300 molecules/cell in log phase SD medium. Belongs to the NifU family.