The yeast inositol-sensitive upstream activating sequence, UASINO, responds to nitrogen availability

The INO1 gene of yeast is expressed in logarithmically growing, wild-type cells when inositol is absent from the medium. However, the INO1 gene is repressed when inositol is present during logarithmic growth and it is also repressed as cells enter stationary phase whether inositol is present or not. In this report, we demonstrate that transient nitrogen limitation also causes INO1 repression. The repression of INO1 in response to nitrogen limitation shares many features in common with repression in response to the presence of inositol. Specifically, the response to nitrogen limitation is dependent upon the presence of a functional OPI1 gene product, it requires ongoing phosphatidylcholine biosynthesis and it is mediated by the repeated element, UASINO, found in the promoter of INO1 and other co-regulated genes of phospholipid biosynthesis. Thus, we propose that repression of INO1 in response to inositol and in response to nitrogen limitation occurs via a common mechanism that is sensitive to the status of ongoing phospholipid metabolism.