Epidemiological studies have suggested that an excess intake of trans-unsaturated fatty acids increases the risk of coronary heart disease. However, the mechanisms of action of trans-unsaturated fatty acids in eukaryotic cells remain unclear. Since the budding yeast Saccharomyces cerevisiae can grow using fatty acids as the sole carbon source, it is a simple and suitable model organism for understanding the effects of trans-unsaturated fatty acids at the molecular and cellular levels. In this study, we compared the physiological effects of Delta 9 cis and trans 18-carbon monoenoic fatty acids (oleic acid and elaidic acid) in yeast cells. The results obtained revealed that the two types have distinct effects on the expression of OLE1, which encodes Delta 9 desaturase, and lipotoxicity in are1 Delta are2 Delta dga1 Delta lro1 Delta and gat1 Delta cells. Our results suggest that cis and trans 18-carbon monoenoic fatty acids exert different physiological effects in the regulation of gene expression and processing of excess fatty acids in yeast. (C) 2016, The Society for Biotechnology, Japan. All rights reserved.