Fig. 5.

Transcriptional regulation of lipid synthesis in yeast. OPI1p is a critical repressor of lipid synthesis in yeast. It is anchored in the ER membrane through its interaction with Scs2p (reviewed in [185]). Inositol starvation activates INO2p–INO4p lipogenic transcription factors by preventing the release of OPI1p from the ER which antagonizes INO2p. Inositol starvation also activates the UPR. INO1 expression is impaired in IRE1 or HAC1 mutant yeasts, which display inositol auxotrophy. The mechanism by which the UPR contributes to the expression of lipogenic genes is not fully understood