DNA microarray technology enables genome-wide detection of cell response at the transcriptional level. We are planning to make bioassay systems that can detect environmental chemicals to screen for potential bioreactive agents. To develop a DNA microarray for our purposes, the changes in gene expression underlying the yeast stress response to cadmium were analyzed by a microarray of total mRNA. Cadmium is a potent cell poison known to cause oxidative stress by changing intracellular glutathione levels. We report here that not only the glutathione synthesis gene (GSH1) but also almost all transcripts of the enzymes involved in the sulfur amino acid metabolism, especially MET14 and MET17, were greatly induced after exposure to cadmium. While several common stress-responsive genes, such as HSP26, GRE1, HSP12, and DDR48, were up-regulated more than almost fourfold by cadmium, there were also 42 other genes up-regulated more than fourfold. Based on these results, we concluded that DNA microarrays are very useful instruments for creating new bioassay systems and finding genetic promoters of stress indicators.

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Adaptation to temperature fluctuation is essential for the survival of all living organisms. Although extensive research has been done on heat and cold shock responses, there have been no reports on global responses to cold shock below 10 degrees C or near-freezing. We examined the genome-wide expression in Saccharomyces cerevisiae, following exposure to 4 degrees C. Hierarchical cluster analysis showed that the gene expression profile following 4 degrees C exposure from 6 to 48 h was different from that at continuous 4 degrees C culture. Under 4 degrees C exposure, the genes involved in trehalose and glycogen synthesis were induced, suggesting that biosynthesis and accumulation of those reserve carbohydrates might be necessary for cold tolerance and energy preservation. The observed increased expression of phospholipids, mannoproteins, and cold shock proteins (e.g., TIP1) is consistent with membrane maintenance and increased permeability of the cell wall at 4 degrees C. The induction of heat shock proteins and glutathione at 4 degrees C may be required for revitalization of enzyme activity, and for detoxification of active oxygen species, respectively. The genes with these functions may provide the ability of cold tolerance and adaptation to yeast cells.

Me 2 SO is a polar solvent that is widely used in biochemistry, pharmacology, and industry. Although there are several reports in the literature concerning the biological effects of Me 2 SO, the total cellular response remains unclear. In this paper, DNA microarray technology combined with the hierarchical clustering bioinformatics tool was used to assess the effects of Me 2 SO on yeast cells. We found that yeast exposed to Me 2 SO increased phospholipid biosynthesis through up-regulated gene expression. It was confirmed by Northern blotting that the level of INO1 and OPI3 gene transcripts, encoding key enzymes in phospholipid biosynthesis, were significantly elevated following treatment with Me 2 SO. Furthermore, the phospholipid content of the cells increased during exposure to Me 2 SO as shown by conspicuous incorporation of a lipophilic fluorescent dye (3,3 -dihexyloxacarbocyanine iodide) into the cell membranes. From these results we propose that Me 2 SO treatment induces membrane proliferation in yeast cells to alleviate the adverse affects of this chemical on membrane integrity.Dimethyl sulfoxide (Me 2 SO) 1 is widely used as a solvent in the chemical industry and as a cryoprotectant in biotechnology. It is present in the environment as a waste product of the paper industry and from the production of dimethyl sulfide (DMS) and also arises from the degradation of sulfur-containing pesticides (1). In addition, Me 2 SO forms naturally from photooxidation of DMS in the atmosphere and from degradation of DMS by phytoplankton in the marine environment (2). Because Me 2 SO has low volatility and is highly hygroscopic, it is rapidly scavenged from the atmosphere by rain and returned to earth, and thereby plays a role in the global sulfur cycle (1, 3).Microorganisms, including both prokaryotes and eukaryotes, have the capability of reducing Me 2 SO and can utilize it as a terminal electron acceptor during anaerobic growth (4 -6). Me 2 SO reductase from Escherichia coli and Rhodobacter sphaeroides catalyzes the reduction of Me 2 SO to DMS (7-9). This enzyme, which contains a molybdenum cofactor at the active center, is well characterized at the biochemical, biophysical, and molecular level and provides an excellent model system for investigating the structure and mechanism of electron transfer chain complexes (1, 10). Saccharomyces cerevisiae has a number of NADPH-dependent enzymes that, in conjunction with methionine sulfoxide reductase (MXR1), can reduce Me 2 SO to DMS (11).In E. coli, the combination of divalent cations as Ca 2ϩ and Me 2 SO has been shown to stimulate the efficiency of DNA transfer into the cell (12). In the case of mammalian cells, it is reported that the transfection efficiency is increased by Me 2 SO treatment after electroporation (13). The exact mechanism of how Me 2 SO increases membrane permeability leading to DNA uptake is unclear.In mammalian cells Me 2 SO (2% (v/v)) can induce morphological changes, for example in mouse erythroleukemic cells (14), or cause differentiation, for example ...

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