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Defective mitosis due to a mutation in the gene for a fission yeast 26S protease subunit
Abstract:
We have isolated a mutant, mts2, in the fission yeast Schizosaccharomyces pombe which is defective in chromosome segregation. The predicted amino-acid sequence of the cloned mts2+ gene product is 75% identical to the S4 subunit of the human 26S ATP/ubiquitin-dependent protease. The human S4 subunit complementary DNA expressed from an S. pombe expression plasmid can rescue an S. pombe mts2 gene disruption. Both observations demonstrate that the mts2+ gene is the S. pombe homologue of the human S4 subunit. In addition, we provide genetic evidence for a physical interaction between the S4 and the related S7 subunit in the 26S multiprotein protease. We show that polyubiquitin-conjugated proteins accumulate in the mts2 mutant at the restrictive temperature, demonstrating that the mutant has an in vivo defect in the ubiquitin-dependent proteolysis pathway. Finally, the phenotype for the mts2 mutant indicates that protein degradation by the 26S protease is essential not for entry into but for the completion of mitosis.
Insights
We identified the mts2 mutant in fission yeast, revealing its role in chromosome segregation. This mutant shows defects in the ubiquitin-dependent proteolysis pathway, essential for mitosis completion.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- Chromosome segregation is crucial for cell division.
- The 26S proteasome is a multi-subunit protein complex involved in protein degradation.
- Ubiquitin-dependent proteolysis plays a role in various cellular processes.
Purpose of the Study:
- To characterize the fission yeast mts2 mutant.
- To investigate the function of the mts2+ gene product.
- To elucidate the role of the 26S proteasome in mitosis.
Main Methods:
- Gene cloning and sequencing of the mts2+ gene.
- Complementation analysis using human S4 subunit cDNA.
- Genetic interaction studies.
- Analysis of polyubiquitin-conjugated proteins.
Main Results:
- The mts2+ gene encodes a homolog of the human 26S proteasome S4 subunit.
- The human S4 subunit can rescue the mts2 mutant phenotype.
- Genetic evidence suggests interaction between S4 and S7 subunits.
- Polyubiquitin-conjugated proteins accumulate in the mts2 mutant.
- The mts2 mutant is defective in ubiquitin-dependent proteolysis.
Conclusions:
- The mts2+ gene is essential for the function of the 26S proteasome in Schizosaccharomyces pombe.
- Protein degradation by the 26S proteasome is required for the completion of mitosis.
- The study provides insights into the role of the ubiquitin-proteasome system in cell cycle regulation.