Similar genes for a mitochondrial ATPase subunit in the nuclear and mitochondrial genomes of Neurospora crassa

Abstract

The proton-translocating ATPases from mitochondria, chloroplasts and bacteria consist of ∼10 different polypeptide subunits¹. The smallest subunit, a proteolipid of molecular weight ∼8,000, is present in a stoichiometric amount of six—these six polypeptides are thought to form a proton channel through the membrane². The proteolipid is affected by the ATPase inhibitors oligomycin and dicyclohexylcarbodiimide (DCCD). As DCCD is covalently bound to it, the proteolipid is commonly referred to as the DCCD-binding protein. Because of the spatial arrangement of the proteolipids in the membrane, binding is probably restricted to one specific glutamic acid residue^2,3. In the yeast Saccharomyces cerevisiae the DCCD-binding protein is encoded by the mitochondrial DNA and synthesized inside the mitochondria⁴, whereas in Neurospora crassa, another ascomycete, the gene for the DCCD-binding protein lies in the nucleus, and the protein is synthesized outside the mitochondria⁵. Here we report the presence on the mitochondrial DNA of N. crassa of a nucleotide sequence which potentially encodes another DCCD-binding protein. Although a translation product has not yet been found, we suggest a possible function of this gene and speculate on its evolutionary origin.