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MRM2 encodes a novel yeast mitochondrial 21S rRNA methyltransferase
Lionel Pintard1, Janusz M Bujnicki, Bruno Lapeyre
1Centre de Recherche de Biochimie Macromoléculaire, CNRS, Montpellier, France.
Abstract:
Mitochondria of the yeast Saccharomyces cerevisiae assemble their ribosomes from ribosomal proteins, encoded by the nuclear genome (with one exception), and rRNAs of 15S and 21S, encoded by the mitochondrial genome. Unlike cytoplasmic rRNA, which is highly modified, mitochondrial rRNA contains only three modified nucleotides: a pseudouridine (Psi(2918)) and two 2'-O-methylated riboses (Gm(2270) and Um(2791)) located at the peptidyl transferase centre of 21S rRNA. We demonstrate here that the yeast nuclear genome encodes a mitochondrial protein, named Mrm2, which is required for methylating U(2791) of 21S rRNA, both in vivo and in vitro. Deletion of the MRM2 gene causes thermosensitive respiration and leads to rapid loss of mitochondrial DNA. We propose that Mrm2p belongs to a new class of three eukaryotic RNA-modifying enzymes and is the orthologue of FtsJ/RrmJ, which methylates a nucleotide of the peptidyl transferase centre of Escherichia coli 23S rRNA that is homologous to U(2791) of 21S rRNA. Our data suggest that this universally conserved modified nucleotide plays an important function in vivo, possibly by inducing conformational rearrangement of the peptidyl transferase centre.
Insights
A newly discovered yeast protein, Mrm2, is essential for methylating a specific nucleotide in mitochondrial ribosomal RNA (rRNA). This modification is crucial for mitochondrial function and stability, impacting respiration and mitochondrial DNA maintenance.
Area of Science:
- Mitochondrial biology
- RNA modification
- Ribosome biogenesis
Background:
- Yeast mitochondria synthesize ribosomes using nuclear and mitochondrial gene products.
- Mitochondrial ribosomal RNA (rRNA) has limited modifications compared to cytoplasmic rRNA.
- Specific modifications in the peptidyl transferase center of 21S rRNA are critical for function.
Purpose of the Study:
- To identify the nuclear-encoded factor responsible for methylating U2791 in yeast mitochondrial 21S rRNA.
- To investigate the in vivo and in vitro function of this methyltransferase.
- To understand the role of this specific rRNA modification in mitochondrial ribosome function and stability.
Main Methods:
- Gene deletion analysis of the MRM2 gene in Saccharomyces cerevisiae.
- In vivo and in vitro methylation assays.
- Assessment of respiratory function and mitochondrial DNA stability in MRM2 deletion mutants.
Main Results:
- The nuclear gene MRM2 encodes a mitochondrial protein, Mrm2p, essential for U2791 methylation of 21S rRNA.
- Deletion of MRM2 results in thermosensitive respiration and rapid loss of mitochondrial DNA.
- Mrm2p is functionally and structurally related to bacterial FtsJ/RrmJ methyltransferases.
Conclusions:
- Mrm2p represents a novel class of eukaryotic RNA-modifying enzymes.
- The methylation of U2791 in 21S rRNA is vital for mitochondrial ribosome function and stability.
- This conserved modification likely induces conformational changes in the peptidyl transferase center, impacting protein synthesis.