Structural and Functional Analyses of the Genes for Subunit II of Cytochrome aa3 and for a Dicyclohexylcarbodiimide-binding Protein in Neurospora crassa Mitochondrial DNA

Abstract

The use of well-defined fragments of yeast mitochondrial genes as probes in hybridization has made it possible to localize protein genes in Neurospora crassa mtDNA (Agsteribbe et al. 1980; Macino 1980). In addition to the positions of the genes for subunits I, II, and III of cytochrome aa₃, for cytochrome b, and for the 19,000-dalton subunit of mitochondrial ATPase, we have discovered a sequence homologous to the gene for the yeast mitochondrial dicyclohexylcarbodiimide (DCCD)-binding protein, also referred to as the ATPase proteolipid. This sequence was found in close proximity to the gene for subunit II of cytochrome aa₃. The presence in Neurospora mtDNA of the former sequence is intriguing, since it has been demonstrated that in Neurospora the ATPase proteolipid is coded by a nuclear gene (Sebald et al. 1979). To establish whether the Neurospora mitochondrial sequence is a nonfunctional gene for an ATPase proteolipid or whether it codes for a related protein and to verify the presence of the gene for subunit II of cytochrome aa₃, we have determined their respective base sequences and have investigated transcription from this region.

RESULTS AND DISCUSSION
The gene for subunit II of cytochrome aa₃ and the sequence homologous to the yeast mitochondrial gene for the ATPase proteolipid are located in EcoRI fragment 4 of Neurospora mtDNA. As a first step toward base sequence analysis and transcription mapping, we have constructed a map of this fragment (Fig. 1).

Base sequence analysis of part of the Neurospora subunit-II gene showed an overall homology of...