Transcriptional Regulation of OLE1 expression in Saccharomyces cerevisiae is Dependent on Fatty Acid Species
Dr. Virginia McDonough
The OLE1 gene in Saccharomyces cerevisiae encodes the ∆9 desaturase, which inserts a double bond in saturated fatty acids to create unsaturated fatty acids (UFAs). OLE1 expression is controlled in part through the transcriptional regulators Mga2p and Spt23p in response to supply of UFAs. We investigated whether the regulation was consistent in response to varied UFA type and concentration. We found that in wild type cells, reporter gene assays show a stronger decrease in expression of OLE1 when fed 16:1∆9 or 18:2∆9, 12 as opposed to 18:1∆9 or 17:1∆10. Concentration of the fed fatty acid also impacted the regulation of OLE1 with higher levels of each UFA impacting expression to a greater degree. Fatty acid profiles of wild type cells show cells accumulate a higher concentration of 16:1∆9 and 18:2∆9, 12 than fed 18:1∆9 or 17:1∆10. This leads to the conclusion that the expression of OLE1 is dependent both on properties of fed fatty acids and the amount in the cell. While our initial hypothesis was that OLE1 is regulated in response to membrane fluidity, subsequent work does not support that idea. Conditions that would affect membrane fluidity (besides UFA species and amount), such as growth temperature and saturated or trans fatty acid supplementation do not regulate OLE1 in the direction predicted by fluidity changes. Recently our lab has isolated a mutant that is deficient in regulation of OLE1, called NRO2 (no regulation of OLE1). The signaling mechanism for the NRO2 protein’s action is unknown. Tests using the OLE1 promoter-reporter gene constructs suggest that NRO2p responds more strongly to the fatty acids 16:1∆9 and 18:2∆9, 12, than 18:1∆9 and 17:1∆10. Efforts are currently underway to clone and identify NRO2.
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