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A yeast nuclear gene, MRS1, involved in mitochondrial RNA splicing: nucleotide sequence and mutational analysis of
Abstract:
We have cloned a 1.6-kb fragment of yeast nuclear DNA, which complements pet- mutant MK3 (mrs1). This mutant was shown to be defective in mitochondrial RNA splicing: the excision of intron 3 from the mitochondrial COB pre-RNA is blocked. The DNA sequence of the nuclear DNA fragment revealed two open reading frames (ORF1 with 1092 bp; ORF2 with 735 bp) on opposite strands, which overlap by 656 bp. As shown by in vitro mutagenesis, ORF1, but not ORF2, is responsible for complementation of the splice defect. Hence, ORF1 represents the nuclear MRS1 gene. Disruption of the gene (both ORFs) in the chromosomal DNA of the respiratory competent yeast strain DBY747 (long form COB gene) leads to a stable pet- phenotype and to the accumulation of the same mitochondrial RNA precursors as in strain MK3. The amino acid sequence of the putative ORF1 product does not exhibit any homology with other known proteins, except for a small region of homology with the gene product of another nuclear yeast gene involved in mitochondrial RNA splicing, CBP2. The function of the MRS1 (ORF1) gene in mitochondrial RNA splicing and the significance of the overlapping ORFs in this gene are discussed.
Insights
Researchers identified the nuclear MRS1 gene in yeast, crucial for mitochondrial RNA splicing. This gene corrects defects in intron removal, ensuring proper mitochondrial function and preventing respiratory deficiency.
Area of Science:
- Molecular Biology
- Yeast Genetics
- Mitochondrial Biology
Background:
- Mitochondrial gene expression relies on RNA processing.
- Mutations in nuclear genes can disrupt mitochondrial RNA splicing.
- The yeast pet- mutant MK3 (mrs1) exhibits a defect in mitochondrial RNA splicing.
Purpose of the Study:
- To clone and characterize the nuclear gene responsible for complementing the yeast pet- mutant MK3 (mrs1).
- To elucidate the function of the identified gene in mitochondrial RNA splicing.
Main Methods:
- Cloning of a yeast nuclear DNA fragment complementing the mrs1 mutant.
- DNA sequencing to identify open reading frames (ORFs).
- In vitro mutagenesis to determine the functional ORF.
- Gene disruption in a wild-type yeast strain to assess phenotypic consequences.
Main Results:
- A 1.6-kb DNA fragment complemented the mrs1 mutant.
- Two overlapping ORFs (ORF1 and ORF2) were identified; ORF1 (1092 bp) was responsible for complementation.
- ORF1 represents the nuclear MRS1 gene.
- Disruption of MRS1 caused a stable pet- phenotype and accumulation of mitochondrial RNA precursors.
- The MRS1 gene product shows limited homology to CBP2, another nuclear gene involved in mitochondrial RNA splicing.
Conclusions:
- The nuclear MRS1 gene is essential for the excision of intron 3 from mitochondrial COB pre-RNA.
- The MRS1 gene product plays a critical role in yeast mitochondrial RNA splicing.
- The study discusses the significance of overlapping ORFs within the MRS1 gene locus.