Involved in the assembly of mitochondrial NADH:ubiquinone oxidoreductase complex (complex I) (By similarity). May be involved in cell proliferation and survival of hormone-dependent tumor cells. May be a regulator of breast tumor cell invasion (By similarity). Binds calmodulin. Interacts with NDUFAF3. Phosphorylated on serine. Prolactin stimulate serine phosphorylation (By similarity). Belongs to the NDUFAF4 family.