A Transcriptional Regulatory System of theS. cerevisiae OLE1Gene Responds to Fatty Acid Species and Intracellular Amount, and not Simply Membrane Status

We examined the effects of unsaturated fatty acid (UFA) species and their concentration on the expression ofOLE1,which encodes the stearoyl CoA desaturase, inSaccharomyces cerevisiae. We controlled the amount of UFA taken up by the cell by varying the concentration of tergitol in the medium. When cultured with 1 mM fatty acid in 0.1% tergitol, cells took up much more fatty acid than when cultured with the same concentration of fatty acid at 1% tergitol, although the amount incorporated was dependent on UFA species. For each fatty acid tested, we found that the higher uptake (0.1% tergitol condition) had a stronger impact onOLE1regulation. A principal product of the desaturase 16:1∆9, and the nonnative UFA 18:2∆9,12, most strongly repressed the reporter constructOLE1-lacZtranscription, while the other major product of the desaturase, 18:1∆9, and the nonnative UFA 17:1∆10 caused a more diminished response. Based on these results, our initial hypothesis was thatOLE1was regulated in response to membrane fluidity; however, subsequent work does not support that idea; we have found that conditions that affect membrane fluidity such as growth temperature and growth with saturated ortransfatty acid supplementation, do not regulateOLE1in the direction predicted by fluidity changes. We conclude that at least one signal that regulatesOLE1transcriptional expression is most likely based on the fatty acids themselves.