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Nuclear and mitochondrial suppression of a mitochondrially inherited cold-sensitive mutation in Aspergillus nidulans
Abstract:
Partial suppressors of a mitochondrially inherited mutation, [cs-67], conferring cold-sensitivity at 20 degrees C were identified. These mapped at one mitochondrial and four unlinked nuclear loci. Most suppressors partially restored the cytochrome aa3 deficiency of the cold-sensitive strain at 20 degrees C. Strains carrying two or more suppressors and [cs-67] showed considerably impaired growth. This effect was temperature-dependent, being more severe at 37 degrees C, and was not expressed in the presence of the [cs-67+] allele. The cytochrome oxidase activity of one of these strains was no more heat-sensitive than that of the wild-type implying that these mutations did not directly modify cytochrome oxidase. The wild-type strain grown in the presence of chloramphenicol and the cold-sensitive strain grown at 20 degrees C had similar cytochrome spectra and mitochondrial membrane protein profiles on sodium dodecyl sulphate gradient acrylamide gels. [cs-67] conferred pleiotropically a low level of resistance to paramomycin at 37 degrees C. It is suggested that [cs-67] and the suppressors act at the level of the mitochondrial ribosome.
Insights
Researchers identified genetic suppressors for a cold-sensitive mitochondrial mutation [cs-67]. These suppressors partially restore cytochrome aa3 deficiency but cause impaired growth when combined with the mutation, suggesting action at the mitochondrial ribosome.
Area of Science:
- Mitochondrial genetics
- Molecular biology
- Cellular respiration
Background:
- Mitochondrial mutations can cause cellular defects, such as cold-sensitivity.
- Understanding suppressors of these mutations provides insights into mitochondrial function and genetic interactions.
Purpose of the Study:
- To identify and characterize partial suppressors of the [cs-67] cold-sensitive mitochondrial mutation.
- To investigate the mechanism by which these suppressors and the mutation affect cellular processes.
Main Methods:
- Genetic mapping of suppressors to identify their loci (mitochondrial and nuclear).
- Biochemical assays to measure cytochrome aa3 deficiency and cytochrome oxidase activity.
- Analysis of mitochondrial membrane protein profiles using SDS-PAGE.
- Phenotypic analysis of growth under different temperature conditions.
Main Results:
- Identified suppressors mapping to one mitochondrial and four nuclear loci.
- Most suppressors partially restored cytochrome aa3 deficiency at 20°C.
- Combinations of suppressors and [cs-67] led to temperature-dependent growth impairment, more severe at 37°C.
- Cytochrome oxidase was not directly modified, and protein profiles were similar to wild-type under specific conditions.
- [cs-67] conferred paramomycin resistance, suggesting a role in mitochondrial translation.
Conclusions:
- The identified suppressors and the [cs-67] mutation likely act at the level of the mitochondrial ribosome.
- Genetic interactions between mitochondrial and nuclear factors influence mitochondrial function.
- The study provides a framework for understanding mitochondrial ribosome function and its regulation.