title: A novel extranuclear mutant of Neurospora with a temperature-sensitive defect in mitochondrial protein synthesis and mitochondrial ATPase.
abstract: [C93] is a novel, extranuclear mutant of Neurospora crassa which has a normal mitochondrial phenotype when grown at 25 degrees, but which is deficient in cytochromes b and aa3 when grown at 37 degrees (Pittenger and West 1979). In the present work, the phenotype of [C93] was characterized in greater detail. When [C93] is grown at 37 degrees, the rate of mitochondrial protein synthesis is decreased to approximately 25% that of wild type; the ratio of mitochondrial small to large ribosomal subunits is decreased to 1:4 and mitochondrial small subunits are deficient in the mitochondrially-synthesized protein, S-5. The mitochondrial ribosome assembly defects in 37 degrees-grown [C93] resemble those in chloramphenicol-treated wild-type cells and could merely be a consequence of the decreased rate of mitochondrial protein synthesis. Analysis of mitochondrial translation products by SDS gel electrophoresis suggests that 37 degrees-grown [C93] is grossly deficient in the 19,000 Mr subunit of the oligomycin-sensitive ATPase relative to other mitochondrially-synthesized proteins. The ATPase defect was not found in other extranuclear or nuclear mutants deficient in mitochondrial protein synthesis. These data and additional evidence suggest that the primary defect in [C93] may be in the assembly of the ATPase complex. The possible connection between the ATPase defect and the deficiency of mitochondrial protein synthesis is discussed.
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics*; D003573:Cytochrome b Group; D003580:Cytochromes / Q000235:genetics; D003576:Electron Transport Complex IV / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D005656:Fungal Proteins / Q000096:biosynthesis* / Q000235:genetics; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism; D009154:Mutation; D009491:Neurospora / Q000235:genetics*; D009492:Neurospora crassa / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D009840:Oligomycins / Q000494:pharmacology; D012270:Ribosomes / Q000648:ultrastructure; D013696:Temperature
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D005656:Fungal Proteins; D009840:Oligomycins; D003576:Electron Transport Complex IV; D000251:Adenosine Triphosphatases