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Chromosomal superkiller mutants of Saccharomyces cerevisiae
Abstract:
Yeast strains carrying a 1.5 X 10(6)-dalton double-stranded RNA in virus-like particles secrete a protein toxin which is lethal to strains not carrying this species of double-stranded RNA. We find that recessive mutations in any of four chromosomal genes result in the superkiller phenotype, i.e., increased secretion of killer toxin activity by strains carrying the killer genome. These genes are designated ski1 through ski4 (for superkiller), ski3 and ski4 are located on chromosome XIV, and ski1 is on chromosome VII. A ski1 mutation results in a decreased rate of cell growth. The kex1 and kex2 mutations are epistatic to each ski mutation.
Insights
Yeast strains with a specific double-stranded RNA (dsRNA) produce a killer toxin. Mutations in four "superkiller" (ski) genes enhance this toxin secretion, impacting yeast killer phenotypes.
Area of Science:
- Molecular biology
- Yeast genetics
- Virology
Background:
- Yeast strains carrying specific double-stranded RNA (dsRNA) in virus-like particles secrete a protein toxin.
- This toxin is lethal to yeast strains lacking the dsRNA, defining the 'killer' phenotype.
Purpose of the Study:
- To investigate genetic factors influencing killer toxin secretion in yeast.
- To identify and characterize genes involved in regulating the killer phenotype.
Main Methods:
- Analysis of yeast strains with mutations in chromosomal genes.
- Phenotypic characterization of killer toxin secretion and cell growth rates.
- Genetic analysis including epistasis tests.
Main Results:
- Recessive mutations in four chromosomal genes (ski1-ski4) result in the "superkiller" phenotype, characterized by increased toxin secretion.
- Genes ski3 and ski4 are located on chromosome XIV; ski1 is on chromosome VII.
- A ski1 mutation also leads to a reduced cell growth rate.
- Mutations kex1 and kex2 were found to be epistatic to ski mutations.
Conclusions:
- The identified ski genes play a crucial role in regulating killer toxin secretion.
- Genetic interactions reveal complex pathways controlling the yeast killer phenomenon.
- Specific mutations can enhance toxin production but may also affect cellular fitness.