NDUFAF1 is a complex I assembly factor protein. Complex I (NADH-ubiquinone oxidoreductase) catalyzes the transfer of electrons from NADH to ubiquinone (coenzyme Q) in the first step of the mitochondrial respiratory chain, resulting in the translocation of protons across the inner mitochondrial membrane. The protein is required for assembly of complex I, and mutations in this protein are a cause of mitochondrial complex I deficiency.