Differential regulatory response for the Δ9 desaturase in Saccharomyces cerevisiae based on fatty acid species and intracellular amount (1000.3)

Abstract

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 uniform in response to different UFAs and at different concentrations. 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. We have found that 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 nro1 (no regulation of OLE1). The signaling mechanism for the NRO1 protein’s action is unknown. Tests using the OLE1 promoter‐reporter gene constructs suggest that Nro1p responds more strongly to the fatty acids 16:1∆9 and 18:2∆9, 12, than 18:1∆9 and 17:1∆10. Characterization of NRO1 is discussed. Grant Funding Source: Supported by NSF‐REU DBI‐0754293