May be involved in cell proliferation and survival of hormone-dependent tumor cells. Involved in the assembly of mitochondrial NADH:ubiquinone oxidoreductase complex (complex I) (By similarity). Binds calmodulin. Interacts with NDUFAF3. Expression is low in quiescent cells and is induced in exponentially proliferating cultures. Expression is also induced when prolactin is added to stationary cells. Induced by dietary differentiating agents such as butyrate, vitamin D3, and retinoic acid. Phosphorylated on serine. Prolactin stimulate serine phosphorylation. Belongs to the NDUFAF4 family.