We performed genome-wide expression analysis to determine genetic responses in Saccharomyces cerevisiae to a low temperature environment using a cDNA microarray. Approximately 25% of the genes in the yeast genome were found to be involved in the response of yeast to low temperature. This finding of a large number of genes being involved in the response to low temperature enabled us to give a functional interpretation to the genetic responses to the stimulus. Functional and clustering analyses of temporal changes in gene expression revealed that global states of the expressions of up-regulated genes could be characterized as having three phases (the early, middle, and late phases). In each phase, genes related to rRNA synthesis, ribosomal proteins, or several stress responses are time-dependently up-regulated, respectively. Through these phases, yeast cells may improve reduced efficiency of translation and enhance cell protection mechanisms to survive under a low temperature condition. Furthermore, these time-dependent regulations of these genes would be controlled by the cAMP-protein kinase A pathway. The results of our study provide a global description of transcriptional response for adaptation to low temperature in yeast cells.Low temperatures are known to have several effects on biochemical and physiological properties in various cells (e.g. low efficiency of protein translation, low fluidity of cellular membrane, stabilization of double helix or secondary structure of DNA or RNA molecule, slow folding of protein, and decrease of enzymatic activities) (1-3). Most organisms would have developed adaptive mechanisms to cope with these phenomena. The mechanisms underlying low temperature-dependent gene expression and responses to low temperature have been studied in few organisms (4 -6).In prokaryotes, especially Escherichia coli, when cells grown at 37°C are exposed to a low temperature, such as 15°C, a set of proteins called cold shock proteins are transiently induced (7). CspA has been identified as a major cold shock protein (8) and has been suggested to act as an RNA chaperone to increase efficiency of translation under a low temperature condition (9). It has been reported that Bacillus and Synechococcus species increase synthesis and stability of desaturases, which catalyze unsaturation of fatty acids in the membrane phopholipids under a low temperature condition (4, 10). Induction of desaturases by low temperature has also been found in eukaryotic species, such as plants (5, 6), protozoan (12), dimorphic fungus (13), fish (14), and yeast (15). These findings suggest that cellular responses to low temperature, such as improvement of reduced translation and decreased membrane fluidity, and their mechanisms are common in various organisms.In yeast, Saccharomyces cerevisiae, several cold-inducible genes have been identified. NSR1, one of the cold-inducible genes, encodes a nucleolin-like protein related to rRNA processing and ribosomal biosynthesis (16 -18). TIP1 (temperatureinducible protein) and the other m...

The yeast reporter assay has been widely used in various applications such as detection of endocrine disruptors and analysis of protein-protein interactions by the yeast two-hybrid system. The molecular characteristics of the reporter enzyme are critical determinants for this assay. We herein report the establishment of a novel yeast reporter assay using a secretory luciferase, Cypridina noctiluca luciferase (CLuc), as an alternative to the conventional beta-galactosidase. The CLuc reporter assay in yeast is more sensitive and convenient than the conventional assay. A yeast high-throughput reporter assay was established with a laboratory automation system, and the transcriptional activity of hundreds of yeast promoter fragments was comprehensively determined. Our results indicate that the yeast CLuc reporter assay is a promising tool for large-scale and sensitive analysis in the development of new drugs and in various fields of biotechnology research.

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