Expression of the INO2 regulatory gene of Saccharomyces cerevisiae is controlled by positive and negative promoter elements and an upstream open reading frame

The INO2 gene encodes a transcriptional activator of the phospholipid biosynthetic genes of Saccharomyces cerevisiae. Complete derepression of phospholipid biosynthetic gene expression in response to inositol/choline deprivation requires both INO2 and INO4. Ino2p dimerizes with Ino4p to bind the upstream activating sequence (UAS)(INO) element found in the promoters of the target genes. We have demonstrated previously that transcription from the INO2 promoter is autoregulated 12-fold in a manner identical to that of the target genes. Here, we show that this regulation occurs at the levels of transcription and translation. Transcription accounts for fourfold regulation, whereas translation accounts for an additional threefold regulation. Regulation of transcription requires a UAS(INO) element. Additional promoter elements include an upstream essential sequence (UES) located upstream of the UAS(INO) element and a negative regulatory element in the vicinity of the UAS(INO) element. Regulation of translation is dependent on an upstream open reading frame (uORF) in the INO2 leader. These data support the model that regulatory gene promoters may display unusual organizations and may be subject to multiple levels of regulation. We have shown previously that the UME6 gene positively regulates INO2 expression. Here, we limit the UME6-responsive region of the INO2 promoter to nucleotides -217 to -56.