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In vivo analysis of sequences required for translation of cytochrome b transcripts in yeast mitochondria
T M Mittelmeier1, C L Dieckmann
1Department of Molecular and Cellular Biology, University of Arizona, Tucson 85721.
Abstract:
Respiratory chain proteins encoded by the yeast mitochondrial genome are synthesized within the organelle. Mitochondrial mRNAs lack a 5' cap structure and contain long AU-rich 5' untranslated regions (UTRs) with many potential translational start sites and no apparent Shine-Dalgarno-like complementarity to the 15S mitochondrial rRNA. However, translation initiation requires specific interactions between the 5' UTRs of the mRNAs, mRNA-specific activators, and the ribosomes. In an initial step toward identifying potential binding sites for the mRNA-specific translational activators and the ribosomes, we have analyzed the effects of deletions in the 5' UTR of the mitochondrial COB gene on translation of COB transcripts in vivo. The deletions define two regions of the COB 5' UTR that are important for translation and indicate that sequence just 5' of the AUG is involved in selection of the correct start codon. Taken together, the data implicate specific regions of the 5' UTR of COB mRNA as possible targets for the mitochondrial translational machinery.
Insights
Yeast mitochondrial translation requires specific interactions within the 5' untranslated regions (UTRs) of mRNAs. Deletions in the COB gene 5' UTR identified key regions for translation and start codon selection.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Mitochondrial gene expression in yeast involves unique translational mechanisms.
- Mitochondrial mRNAs lack 5' cap structures and possess long, AU-rich 5' untranslated regions (UTRs).
- Translation initiation in mitochondria is complex, requiring interactions between 5' UTRs, activators, and ribosomes.
Purpose of the Study:
- To identify potential binding sites for translational activators and ribosomes within mitochondrial mRNA 5' UTRs.
- To investigate the role of the 5' UTR of the mitochondrial COB gene in translation initiation.
- To understand the selection mechanism of the correct start codon during mitochondrial translation.
Main Methods:
- Analysis of deletion mutants in the 5' UTR of the yeast mitochondrial COB gene.
- In vivo studies of COB transcript translation.
- Investigating the effects of UTR sequence modifications on protein synthesis.
Main Results:
- Two critical regions within the COB gene 5' UTR were identified as important for translation.
- Sequence elements immediately upstream of the AUG start codon play a role in selecting the correct initiation site.
- Specific regions of the COB mRNA 5' UTR are implicated as targets for the mitochondrial translational machinery.
Conclusions:
- The study provides insights into the regulatory mechanisms of yeast mitochondrial translation.
- Specific sequences within the 5' UTR are essential for efficient and accurate translation initiation.
- This research lays the groundwork for understanding how mRNA-specific activators and ribosomes interact with mitochondrial transcripts.