The nuclear gene MRS2 is essential for the excision of group II introns from yeast mitochondrial transcripts in vivo

Area of Science:

• Mitochondrial genetics
• Molecular biology
• Gene function

Background:

• RNA splicing defects in mitochondria can be compensated by nuclear gene products.
• The MRS2 gene is a nuclear gene implicated in suppressing mitochondrial intron mutations.

Purpose of the Study:

• To isolate and characterize the nuclear MRS2 gene.
• To elucidate the function of the MRS2 gene and its protein product in mitochondrial RNA splicing and function.

Main Methods:

• Gene isolation and nucleotide sequencing of the MRS2 gene.
• Complementation studies using high copy number plasmids expressing MRS2.
• Gene disruption of the chromosomal MRS2 copy.
• Analysis of mitochondrial RNA splicing in wild-type and MRS2-disrupted strains.
• Phenotypic analysis (pet phenotype, cytochrome deficiency) of MRS2 mutants.

Main Results:

• The MRS2 gene suppresses mitochondrial intron mutations when overexpressed.
• Disruption of MRS2 leads to a pet- phenotype and blocks splicing of all four mitochondrial group II introns.
• Group I intron splicing is less affected by MRS2 disruption.
• MRS2 is essential for group II intron splicing but not critical for group I intron splicing.
• MRS2 disruption causes cytochrome deficiency and a pet- phenotype even in intron-less strains, suggesting roles beyond splicing.

Conclusions:

• The MRS2 protein is a vital splicing factor for mitochondrial group II introns.
• The MRS2 protein plays a role in mitochondrial function independent of its splicing activity, potentially in membrane complex assembly.