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 biosy nthetic genes of Saccharomyces cerevisiae. Complete derepression of phospho lipid biosynthetic gene expression in response to inositol/choline deprivat ion requires both INO2 and INO4. Ino2p dimerizes with Ino4p to bind the ups tream activating sequence (UAS)(INO) element found in the promoters of the target genes. We have demonstrated previously that transcription from the I NO2 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 tr anscription and translation. Transcription accounts for fourfold regulation , whereas translation accounts for an additional threefold regulation. Regu lation of transcription requires a UAS(INO) element. Additional promoter el ements 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 ope n reading frame (uORF) in the INO2 leader. These data support the model tha t regulatory gene promoters may display unusual organizations and may be su bject to multiple levels of regulation. We have shown previously that the U ME6 gene positively regulates INO2 expression. Here, we limit the UME6-resp onsive region of the INO2 promoter to nucleotides -217 to -56.