Single point mutations in domain II of the yeast mitochondrial release factor mRF-1 affect ribosome binding
1Department of Molecular Cell Biology, University of Amsterdam, The Netherlands.
Abstract:
We have recently described two yeast strains that are mutated in the MRF1 gene encoding the mitochondrial release factor mRF-1. Both mutants provoke gene-specific defects in mitochondrial translational termination. In the present study we report the cloning, sequencing, as well as an analysis of residual activities of both mutant mrf1 alleles. Each allele specifies a different single amino acid substitution located one amino acid apart. The amino acid changes do not affect the level or cellular localization of the mutant proteins, since equal amounts of wild type and mutant mRF-1 were detected in the mitochondrial compartment. Over-expression of the mutant alleles in wild type and mrf1 mutant yeast strains produces a phenotype consistent with a reduced affinity of the mutant release factors for the ribosome, indicating that the mutations map in a release factor domain involved in ribosome binding. We also demonstrate that nonsense suppression caused by a mutation in the mitochondrial homolog of the E. coli small ribosomal protein S4 can be reversed by a slight over-expression of the MRF1 gene.
Insights
Two yeast strains with mutations in the mitochondrial release factor 1 (mRF-1) gene show defects in mitochondrial translation termination. These mutations affect ribosome binding, impacting protein synthesis.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Mitochondrial translation relies on specific release factors for termination.
- Mutations in the MRF1 gene encoding mitochondrial release factor 1 (mRF-1) cause gene-specific defects in translational termination.
Purpose of the Study:
- To clone, sequence, and analyze the residual activities of two previously identified mutant mrf1 alleles.
- To investigate the functional consequences of these mutations on mRF-1 protein activity and ribosome interaction.
Main Methods:
- Allele cloning and sequencing.
- Analysis of mutant mRF-1 protein levels and localization in yeast mitochondria.
- Phenotypic analysis of yeast strains over-expressing mutant mrf1 alleles.
- Nonsense suppression assays.
Main Results:
- Each mrf1 allele substitution results in a distinct single amino acid change.
- Mutant mRF-1 proteins are stable and correctly localized to mitochondria.
- Over-expression of mutant alleles suggests reduced ribosome binding affinity.
- Mutations likely reside in a ribosome-binding domain of mRF-1.
- MRF1 over-expression can reverse nonsense suppression caused by a mutation in a mitochondrial ribosomal protein.
Conclusions:
- The identified mrf1 mutations impair mitochondrial translational termination by affecting ribosome binding.
- MRF1 plays a crucial role in the fidelity of mitochondrial translation.
- Targeted manipulation of MRF1 expression can potentially correct certain mitochondrial translation defects.
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