This family consists of the MNLL subunits of NADH-ubiquinone oxidoreductase complex. NADH-ubiquinone oxidoreductase is involved in the transfer of electrons from NADH to the electron transport chain. This oxidation of NADH is coupled to proton transfer across the membrane, generating a proton motive force that is utilized for the synthesis of ATP. MNLL subunit is one of the many subunits found in the complex and it contains a mitochondrial import sequence. However, the role of MNLL subunit is unclear.