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mim3 and nam3 omnipotent suppressor genes similarly affect the polypeptide composition of yeast mitoribosomes
1Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw.
Abstract:
Yeast informational suppressors of mit- mutations coded for by nuclear (nam3-1, nam3-2) or by mitochondrial DNA (mim3-1) affect the mitoribosome. Nuclear mutations result in the appearance of an additional polypeptide called SI in the small mitoribosomal subunit. An identical polypeptide, not detected in the wild type 37S subunit, is present in crude preparations of mitoribosomes isolated from a mim3-1 suppressor carrying strain. Traces of the SI polypeptide may be found in highly purified small subunits from the mim3-1 strain. Therefore, mutations affecting either mitochondrial rRNA (mim3-1) or mitochondrial r-proteins (nam3-1, nam3-2) could be followed by similar changes in overall mitoribosome structure. This may explain the functional similarity of nuclear and mitochondrially coded suppressors.
Insights
Nuclear and mitochondrial mutations affecting yeast mitoribosomes lead to similar structural changes. These mutations, impacting mitochondrial ribosomal proteins or RNA, result in an extra polypeptide (SI) in the small subunit, explaining suppressor similarities.
Area of Science:
- Mitochondrial genetics
- Ribosome biogenesis
- Molecular cell biology
Background:
- Yeast informational suppressors of mitochondrial (mit) mutations can arise from nuclear (nam3-1, nam3-2) or mitochondrial DNA (mim3-1).
- These suppressors impact the function and structure of the mitoribosome, the mitochondrion's protein synthesis machinery.
Purpose of the Study:
- To investigate the molecular basis for the functional similarity between nuclear and mitochondrially encoded suppressors of yeast mit- mutations.
- To determine if mutations in nuclear- or mitochondrially encoded genes affecting the mitoribosome lead to comparable structural alterations.
Main Methods:
- Analysis of mitoribosome composition from yeast strains carrying nuclear suppressors (nam3-1, nam3-2) and a mitochondrial suppressor (mim3-1).
- Identification and characterization of specific polypeptides associated with altered mitoribosomal subunits using biochemical approaches.
Main Results:
- Nuclear mutations (nam3-1, nam3-2) induce the presence of an additional polypeptide, termed SI, in the small mitoribosomal subunit.
- Mitochondrial mutations (mim3-1) also result in the appearance of the SI polypeptide in mitoribosome preparations, although in trace amounts in highly purified subunits.
- The SI polypeptide is absent in wild-type yeast mitoribosomes.
Conclusions:
- Mutations affecting either mitochondrial ribosomal proteins (nuclear-encoded) or mitochondrial ribosomal RNA (mitochondrially encoded) can lead to similar changes in mitoribosome structure.
- The presence of the SI polypeptide in both nuclear and mitochondrial suppressor strains provides a molecular explanation for the functional convergence of these genetic elements.