The NADH-ubiquinone oxidoreductase complex (complex I) of the mitochondrial respiratory chain catalyzes the transfer of electrons from NADH to ubiquinone, and consists of at least 43 subunits. The complex is located in the inner mitochondrial membrane. This gene encodes a mitochondrial protein that is associated with the matrix face of the mitochondrial inner membrane and is required for complex I assembly. A mutation in this gene results in mitochondrial complex I deficiency. Multiple transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Oct 2009].