Negative regulator of the transcriptional complex INO2-INO4 in response to phospholipid precursor availability. When precursors become limiting, OPI1 is retained at the endoplasmic reticulum (ER) and INO2-INO4 activates INO1 and other genes required for phospholipid biosynthesis, whereas abundant precursor availability results in targeting of OPI1 to the nucleus to repress transcription of these genes. Binds directly to phosphatidic acid, which is required for ER targeting and may act as sensing mechanism for precursor availability, as phosphatidic acid becomes rapidly depleted upon phospholipid biosynthesis. Interacts with SCS2. Maintained at the endoplasmic reticulum by SCS2 (PubMed:12727870). In response to elevated inositol levels, translocates to the nucleus (PubMed:15192221). The FFAT motif is required for interaction with SCS2 and proper localization of the protein. Present with 1281 molecules/cell in log phase SD medium.