Relationship between a subunit of NADH dehydrogenase (complex I) and a protein family including subunits of cytochrome reductase and processing protease of mitochondria

The primanry structure of a 40 kDa subunit of the respiratory chain NADH:ubiquinone reductase from Neurospora crassawas determined by sequencing cDNA, genomic DNA and the N-terminus of the mature protein. The gene which is interrupted by 7 introns encodes a preprotein consisting of 375 amino acids with a 26 amino acid long presequence typical for a mitochondrial targetting signal. The sequence of the mature subunit shows conspicuous similarities to the recently [(1989) Nature 339, 147–149] discovered protein family which includes subunits I and II of the ubiquinol:cytochrome creductase, and the processing proteins, matrix processing peptidase and processing enhancing protein, of mitochondria. The possible role of the subunit is discussed.