Saccharomyces cerevisiae PHO5 promoter region: location and function of the upstream activation site

Saccharomyces cerevisiae repressible acid phosphatase (PHO5) is induced when inorganic phosphate in the culture medium is depleted. To study the mechanism of this regulation, we constructed various deletions in the 5'-flanking region of the PHO5 gene. Two elements were revealed by this analysis: an upstream activation site (UAS) and a downstream element, both playing parts in the expression of this gene. The UAS is located between -384 and -292 upstream of the initiation codon and activates expression of the gene when inorganic phosphate is depleted. It consists of two homologous regions (UAS I and UAS II) that contain CTGCACAAATG and an adenine-plus-thymine-rich sequence, either one of which suffices for the effect. The downstream element includes a putative TATA box at -100 from the ATG codon and is necessary for efficient transcription and expression of the normal-sized PHO5 transcript. The distance between the UAS and the downstream element can be altered without causing loss of expression efficiency, and the action of the UAS is not affected by its orientation. These results are consistent with a model wherein UAS acts as a site of activation for transcription by interaction with a protein factor(s) that becomes active when inorganic phosphate is depleted from the culture medium.