Core subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I) that is believed to belong to the minimal assembly required for catalysis. Complex I functions in the transfer of electrons from NADH to the respiratory chain. The immediate electron acceptor for the enzyme is believed to be ubiquinone. a ubiquinone + 5 H(+)(in) + NADH = a ubiquinol + 4 H(+)(out) + NAD(+) Part of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I) (By similarity). Interacts with sicily; interaction is stronger with unprocessed sicily protein (PubMed:23509070). Upon mitochondrial dysfunction, the translation of the mRNA occurring on the mitochondrial surface is impaired and amino acids non-coded by the RNA template are added to the C-terminal of the protein. The C-terminal extended proteins aggregates in the cytosol and are toxic. The phenomenon is called mitochondrial-stress induced translational termination impairment and protein carboxyl terminal extension (MISTERMINATE). Belongs to the complex I 30 kDa subunit family.