A, UASINO-containing genes (blue) are maximally expressed (thick arrow) when wild-type S. cerevisiae cells are grown in the absence of inositol and in the presence of sufficient amounts of essential nutrients. B, when inositol is added to the growth medium or when cells are depleted of an essential nutrient, transcription of UASINO-containing genes is attenuated (thin arrow) by the interaction of Opi1p with Ino2p. Dissociation of Opi1p from the nuclear/ER membrane is caused by a decrease in PA concentration, which is mediated by the stimulation of PI synthesis and by activation of Mg2+-dependent PA phosphatase (PAP1, denoted by the star). Etn, ethanolamine; Cho, choline; Ins, inositol.