Dissecting the Regulation of the OLE1 Gene in Saccharomyces Cerevisiae: Examining the Role of Fatty Acid Species and Concentration
Dr. Virginia McDonough
The OLE1 gene product, the delta-9 desaturase, inserts a double bond in saturated fatty acids to create unsaturated fatty acids (UFAs). OLE1 expression is controlled in part through the transcription factors Mga2p and Spt23p in response to the supply of UFAs. These proteins reside in the endoplasmic reticulum, and when insufficient supply of UFAs is detected, they are proteolytically cleaved and translocated into the nucleus, where they activate OLE1 expression. Recently our lab has isolated a mutant that is deficient in regulation of OLE1, called nro1 (no regulation of OLE1). The mechanism for the NRO1 protein’s action is unknown. In this study, growth tests and enzyme assays using reporter genes controlled by the OLE1 promoter region suggest that Nro1p responds more strongly to the fatty acids 16:1 Δ9 and 18:2 Δ9, 12, than 18:1 Δ9 and 17:1 Δ9. When wild type cells are fed 16:1 Δ9 and 18:2 Δ9, 12, fatty acid profiles revealed them present at a higher percentage than when fed other UFAs, probably because endogenous UFA production is more severely curtailed. The concentration of the fed fatty acid also impacted the regulation of OLE1, with higher concentrations bringing about more robust regulation. However, in nro1 cells, there was diminished regulation of expression in response to feeding certain UFAs as compared to wild type cells. Western blot analysis showed no evidence that Mga2p and Spt23p regulate OLE1 through the NRO1 signaling system. We conclude that the expression of OLE1 is dependent on properties of the fed fatty acid, the amount in the cell, and that the NRO1 gene product may be working through other regulatory networks besides Mga2p/Spt23p.
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