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Genetic studies on cycloheximide-resistant strains of Schizosaccharomyces pombe
Abstract:
Cycloheximide-resistant mutants of Schizosaccharomyces pombe were isolated either as spontaneous mutants or after mutagenic treatment with nitrous acid, UV and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Twenty-three spontaneous mutants and 64 induced mutants were analysed genetically. Crosses revealed that at least four loci, designated cyh1, cyh2, cyh3 and cyh4 are responsible for resistance. Alleles of cyh1 show good growth on either high (100 mug/ml) or low (40 mug/ml) concentrations of cycloheximide whereas alleles at the cyh2, cyh3 and cyh4 loci gorw well on 40 mug/ml but poorly on 100 mug/ml. Some alleles at the cyh2 and cyh3 loci are also temperature sensitive (ts), the ts phenotype being conferred by the same gene as the resistance. In diploids, cyh1 and cyh4 are re-essive to wild type whereas cyh2 and cyh3 are semi-dominant. There was no intragenic complementation between three cyh1 alleles. Cross-resistance to trichodermin and anisomycin was shown by cyh2, cyh3 and cyh4 but not cyh1. Most cyh1 alleles, of spontaneous and UV origin only, were cold sensitive (cs) at 14 degrees and some of these were also cycloheximide dependent at the same temperature. It is suggested that the cyh1 and cyh4 genes are involved in ribosome formation or function and the other loci probably affect the uptake of cycloheximide by the cells.
Insights
Researchers identified four genes (cyh1-cyh4) conferring cycloheximide resistance in yeast. Different alleles exhibit varying resistance levels and cross-resistance to other toxins, suggesting roles in ribosome function or drug uptake.
Area of Science:
- * Molecular Genetics
- * Yeast Biology
- * Drug Resistance Mechanisms
Background:
- * Cycloheximide is a potent inhibitor of protein synthesis, widely used to select for resistant mutants.
- * Understanding resistance mechanisms in model organisms like *Schizosaccharomyces pombe* provides insights into cellular processes and potential therapeutic targets.
Purpose of the Study:
- * To genetically characterize cycloheximide-resistant mutants of *Schizosaccharomyces pombe*.
- * To identify the loci responsible for cycloheximide resistance and analyze their inheritance patterns and associated phenotypes.
Main Methods:
- * Isolation of spontaneous and induced cycloheximide-resistant mutants using chemical mutagens (nitrous acid, MNNG) and UV radiation.
- * Genetic analysis through crosses to determine the number of loci and allelic relationships.
- * Phenotypic characterization of mutants, including growth on different cycloheximide concentrations, temperature sensitivity, and cross-resistance assays.
Main Results:
- * Four resistance loci (cyh1, cyh2, cyh3, cyh4) were identified through genetic crosses.
- * Alleles at *cyh1* confer resistance to both high and low cycloheximide concentrations, while *cyh2*, *cyh3*, and *cyh4* alleles are more sensitive to high concentrations.
- * Some *cyh2* and *cyh3* alleles exhibit temperature sensitivity, and *cyh2*, *cyh3*, *cyh4* show cross-resistance to trichodermin and anisomycin.
Conclusions:
- * The identified genes likely play roles in ribosome biogenesis or function (*cyh1*, *cyh4*) or influence cycloheximide uptake (*cyh2*, *cyh3*).
- * Distinct resistance profiles suggest diverse mechanisms contributing to cycloheximide resistance in *S. pombe*.