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Translation of nad9 mRNAs in mitochondria from Solanum tuberosum is restricted to completely edited transcripts
1Institut für Genbiologische Forschung Berlin, Germany.
Abstract:
The pool of partially and completely edited mRNAs present in plant mitochondria could potentially be translated into a mixture of divergent proteins. This possibility was investigated for the nad9 gene in potato by characterization of the mRNA population and the corresponding protein sequence. The deduced amino acid sequence of the nad9 gene product has significant similarity to the nuclear-encoded 30 kDa subunit of the bovine and Neurospora NADH:ubiquinone oxidoreductase (complex I) and to the chloroplast ndhJ gene product. Immunoprecipitation of a 27 kDa in-organello 35S labelled mitochondrial translation product with an antibody directed against the wheat nad9 gene product demonstrates its functional expression in potato and wheat. Comparison of the nad9 genomic DNA and cDNA sequences reveals seven codons to be changed by a C to U RNA-editing. Direct sequencing of RT-PCR products derived from cDNAs of different tissues of potato plants shows the presence of a significant portion of only partially edited nad9 transcripts in the various tissues. Amino acid sequencing of internal peptides of the isolated 27 kDa protein from potato tubers demonstrates homogenous translation products of only completely edited nad9 mRNAs even in the presence of partially edited mRNAs. This result suggests a pretranslational selection between edited and incompletely edited mRNAs in plant mitochondria.
Insights
Plant mitochondria can produce different proteins from edited messenger RNAs (mRNAs). Studies show potato nad9 mRNA is fully edited before translation, suggesting a selection process.
Area of Science:
- Mitochondrial gene expression
- RNA editing in plants
- Plant molecular biology
Background:
- Plant mitochondria contain partially and completely edited mRNAs.
- These edited mRNAs could potentially translate into different proteins.
- The nad9 gene in potato mitochondria was investigated.
Purpose of the Study:
- To investigate the translation of partially and completely edited nad9 mRNAs in potato mitochondria.
- To determine if RNA editing affects protein sequence and function.
- To understand the selection mechanisms for mRNA translation.
Main Methods:
- Characterization of the nad9 mRNA population using RT-PCR and direct sequencing.
- Comparison of genomic DNA and cDNA sequences to identify RNA editing sites.
- Immunoprecipitation of mitochondrial translation products using antibodies.
- Amino acid sequencing of isolated proteins to determine the translated product.
Main Results:
- The deduced amino acid sequence of the potato nad9 gene product shows similarity to known proteins involved in NADH:ubiquinone oxidoreductase (complex I).
- Functional expression of the nad9 gene product was demonstrated in potato and wheat.
- Seven C to U RNA editing events were identified in the nad9 gene.
- Partially edited nad9 transcripts were present in various potato tissues.
- However, only completely edited nad9 mRNAs were translated into homogeneous protein products.
Conclusions:
- Plant mitochondria exhibit a pre-translational selection mechanism.
- This mechanism favors the translation of completely edited nad9 mRNAs.
- RNA editing plays a crucial role in ensuring the production of functional mitochondrial proteins.