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Yeast bZip proteins mediate pleiotropic drug and metal resistance
A Wu1, J A Wemmie, N P Edgington
1Program in Molecular Biology, University of Iowa, Iowa City 52242.
Abstract:
Saccharomyces cerevisiae contains a group of transcription factors related to mammalian c-Jun. This yeast Jun-family of proteins consists of GCN4, a regulator of genes involved in amino acid biosynthesis, and yAP-1, a factor conferring pleiotropic drug resistance when overexpressed. In the work described here, we show that a third member of the yeast Jun-family exists. This protein has been designated CAD1 and provides resistance to cadmium when present on a high-copy plasmid. CAD1 and yAP-1 are related in their amino-terminal DNA binding domains and can recognize the same DNA target site in vitro. Overproduction of CAD1 leads to transcriptional activation of an artificial reporter gene in delta yap1 cells. High level production of either CAD1 or yAP-1 causes cells to acquire a pleiotropic drug-resistant phenotype and to be able to tolerate normally toxic levels of iron chelators and zinc. Surprisingly, disruption of the CAD1 gene has no effect on the normal cellular resistance to cadmium but delta yap1 mutants are hypersensitive to this cytotoxic metal. The cadmium hypersensitivity of the delta yap1 mutant described here indicates that one major role of YAP1 in the yeast cell is to mediate resistance to this metal.
Insights
Researchers discovered CAD1, a new yeast Jun-family transcription factor. CAD1 and YAP1 (yeast AP-1) mediate resistance to toxic metals like cadmium, iron, and zinc, crucial for cellular defense.
Area of Science:
- Molecular Biology
- Yeast Genetics
- Transcription Factor Research
Background:
- Saccharomyces cerevisiae possesses Jun-family transcription factors, including GCN4 and yAP-1.
- yAP-1 confers pleiotropic drug resistance upon overexpression.
- The existence of additional Jun-family members was investigated.
Purpose of the Study:
- To identify and characterize a novel member of the yeast Jun-family of transcription factors.
- To elucidate the function of this new factor, designated CAD1, in cellular resistance mechanisms.
- To compare the functions of CAD1 and yAP-1 in response to toxic substances.
Main Methods:
- Gene disruption and overexpression in Saccharomyces cerevisiae.
- Analysis of transcriptional activation using artificial reporter genes.
- Assessment of cellular resistance to cadmium, iron chelators, and zinc.
Main Results:
- A third yeast Jun-family member, CAD1, was identified, conferring cadmium resistance when overexpressed.
- CAD1 and yAP-1 share DNA binding domain similarities and recognize the same DNA target site.
- Overproduction of CAD1 or yAP-1 results in pleiotropic drug resistance and tolerance to high levels of iron chelators and zinc.
- Disruption of CAD1 had no effect on cadmium resistance, but delta yap1 mutants exhibited hypersensitivity to cadmium.
Conclusions:
- Yeast possesses at least three Jun-family transcription factors: GCN4, yAP-1, and CAD1.
- YAP1 plays a significant role in mediating cellular resistance to cadmium.
- Both CAD1 and yAP-1 contribute to cellular defense mechanisms against toxic metals and other stressors.