THE 12.3 KDA SUBUNIT OF COMPLEX-I (RESPIRATORY-CHAIN NADH DEHYDROGENASE) FROM NEUROSPORA-CRASSA - CDNA CLONING AND CHROMOSOMAL MAPPING OF THE GENE

The 12.3 kDa subunit of complex I (respiratory-chain NADH dehydrogenas e) is a nuclear-coded protein of the hydrophobic fragment of the enzym e. We have isolated and sequenced a full-length cDNA clone coding for this polypeptide. The deduced protein is 104 amino acid residues long with a molecular mass of 12 305 Da. This particular subunit of complex I lacks a cleavable mitochondrial targeting sequence. In agreement wi th its localization within complex I, we have found that this subunit behaves like an intrinsic membrane protein. Nevertheless, the deduced protein is rather hydrophilic, exhibiting no hydrophobic domain long e nough to traverse a membrane in an alpha-helical conformation. The 12. 3 kDa subunit shows a significant similarity to the hinge protein of c omplex III, suggesting that these two polypeptides may be involved in identical functions. This complex I subunit is coded for by a single g ene. Applying restriction-fragment-length-polymorphism mapping, we loc ated the gene on the right side of the centromere in linkage group I, linked to the lys-4 locus.