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Mutagenesis by cytostatic alkylating agents in yeast strains of differing repair capacities
Abstract:
Reversion of two nulcear ochre nonsense alleles and cell inactivation induced by mono-, bi-, and tri-functional alkylating agents and by UV has been investigated in stationary-phase haploid cells of yeast strains with differing capacities for DNA repair. The ability to survive alkylation damage is correlated with UV repair capacity, a UV-resistant and UV-mutable strain (RAD REV) being least and a UV-sensitive and UV-nonmutable strain (radi rev3) most sensitive. Mutagenicity of alkylating agents is highest in the former and is abolished in the latter strain. Deficiency in excision repair (rad1 rad2) or in the RAD18 function does not lead to enhanced mutability. Mutagenesis by the various agents is characterized by a common pattern of induction of locus-specific revertants and suppressor mutants. Induction kinetics are mostly linear, but UV-induced reversion in the RAD REV strain follows higher-than-linear (probably "quadratic") kinetics. The alkylating agent cyclophosphamide, usually considered inactive without metabolic conversion, reduces colony-forming ability and induces revertants in a manner similar but not identical to the other chemicals tested. These findings are taken to support the concept of mutagenesis by misrepair after alkylation, which albeit sharing common features with the mechanism of UV-induced reversion, can be distinguished therefrom.
Insights
DNA repair capacity influences yeast cell survival and mutation rates from alkylating agents and UV radiation. Yeast strains with higher UV repair ability showed increased mutation sensitivity to alkylating agents.
Area of Science:
- Molecular Biology
- Genetics
- Yeast Genetics
Background:
- Cellular responses to DNA damage are crucial for maintaining genomic stability.
- Different DNA repair pathways exist in organisms, varying in efficiency and specificity.
- Understanding mutagenesis mechanisms helps in assessing the risks of chemical and physical mutagens.
Purpose of the Study:
- To investigate the reversion of nonsense mutations and cell inactivation in yeast exposed to alkylating agents and UV radiation.
- To correlate DNA repair capacity with sensitivity and mutagenicity induced by these agents.
- To elucidate the mechanisms of mutagenesis by alkylating agents and UV light in yeast.
Main Methods:
- Utilized stationary-phase haploid yeast strains with varying DNA repair capacities.
- Exposed yeast cells to mono-, bi-, and tri-functional alkylating agents and UV radiation.
- Assessed cell inactivation (survival) and induced reversion of specific nonsense alleles.
Main Results:
- Survival after alkylation damage correlated inversely with UV repair capacity; UV-resistant strains were most sensitive.
- Mutagenicity of alkylating agents was highest in UV-resistant strains and abolished in UV-sensitive strains.
- Mutagenesis followed a common pattern of locus-specific revertants and suppressor mutants, with UV showing quadratic kinetics in proficient strains.
Conclusions:
- Findings support the concept of mutagenesis by misrepair following alkylation damage in yeast.
- The mechanism of mutagenesis by alkylating agents shares features with UV-induced reversion but is distinct.
- Differential DNA repair capacities significantly modulate the genotoxic effects of chemical and physical mutagens.