Mitochondrial ATPase Complex of Aspergillus nidulans and the Dicyclohexylcarbodiimide‐Binding Protein

Abstract

The dicyclohexylcarbodiimide-binding protein of Aspergillus nidulans has been identified as the smallest subunit of the mitochondrial ATPase complex, and has a molecular weight of approximately 8000. It is extractable from whole mitochondria and from the purified enzyme in neutral chloroform/ methanol, contains 30% polar amino acids, and the N-terminal amino acid has been identified as tyrosine. Using a double-labelling technique in the absence and presence of cycloheximide, followed by immunoprecipitation of the enzyme complex with antiserum against Neurospora crassa F1 ATPase, it has been shown that this subunit is synthesized on cytoplasmic ribosomes.Oligomycin-resistant mutants have been isolated in the filamentous Ascomycete Aspergillus nidulans [l ] and mutations in both nuclear and extranuclear genomes have been shown to affect the oligomycin sensitivity of the mitochondria1 ATPase activity [2,3], suggesting the involvement of at least two subunits of the enzyme complex, one nuclearly coded and one extranuclearly coded, in the expression of oligomycin resistance. Furthermore, nuclear-extranuclear interactions have been observed in strains containing mutations in both genomes [3]. In contrast, only extranuclear oligomycin-resistant mutants in Saccharomyces cerevisiae [4,5] and nuclear oligomycin-resistant mutants in Neurospora crassa [6] have been shown to alter the resistance of the ATPase activity of these organisms in vitro.In order to identify the lesions caused by these mutants, and thus the gene-protein relationships, studies on the ATPase complex are essential. Oligomycin is known to inhibit oxidative phosphorylation by acting on the Fo or membrane components of the complex [7]. Dicyclohexylcarbodiimide acts at a nearby site in a similar manner, and shows irreversible binding to one of the FO components [8-111. This hydrophobic polypeptide, referred to as the dicyclohexylcarbodiimide-binding protein, has now been extracted from a number of sources, including the mitochondria of beef heart [ll, 121, S. cerevisiae [13,14] and N . crassa 11.51, the chloroplasts of lettuce [16] and from membranes of Escherichia coli [17]. In all of these species the protein has a molecular weight of

Has the endosymbiont hypothesis been proven?

“…46,1982 on September 1, 2020 by guest http://mmbr.asm.org/ Downloaded from notable exception being the gene for the dicyclohexylcarbodiimide-binding proteolipid of the ATPase complex. In contrast to the situation in yeast, this polypeptide is not made in mitochondria in Neurospora crassa (405), Aspergillus nidulans (444), and animals (122), but is synthesized in and imported from the cytosol. In Neurospora, at least, the proteolipid is a nuclear gene product (406), although there is recent evidence that a "silent" gene or portion thereof may be present in the mtDNA of this organism (1).…”

Structure and evolution of organelle genomes.

“…Two P. aurelia maps are given, one for species 1 also been mapped on Neurospora and Aspergillus mtDNAs. However, in both Aspergillus and Neurospora the DCCD-binding protein is synthesized in the cytosol (189,331,358), and this gene has been located on Neurospora nuclear linkage group VII (331). Since Neurospora mtDNA still retains sequences homologous to the yeast subunit 9 gene, these sequences must represent a subunit 9 pseudogene (1).…”

Two genes encoding the bovine mitochondrial ATP synthase proteolipid specify precursors with different import sequences and are expressed in a tissue-specific manner.

“…As its name implies it is a hydrophobic protein; in bovine mitochondria it is 75 amino acids in length (Sebald and Hoppe, 1981). In mammals (Anderson et al, 1981(Anderson et al, , 1982, Aspergillus nidulans (Turner et al, 1979), Neurospora crassa (Jackl and Sebald, 1975) (but not Saccharomyces cerevisiae; Macino and Tzagoloff, 1979) it is a nuclear gene product. It is presumed that it is synthesised on free ribosomes as a longer precursor, and imported into the mitochondrion in a post-translational process that involves removal of a segment from the N-terminal region of the precursor (Schatz and Butow, 1983;Hay et al, 1984).…”