Analysis of Activation Activity of Yeast PHO2, PHO4 Protein and Their Interaction

Both PHO2 and PHO4 are positive regulatory factors of yeast PHO5 gene. Here we show that the PHO2 fused to yeast transcriptional factor GAL4 DNA-binding domain activates the expression of the reporter gene (lacZ), and the lacZ activities were regulated by Pi concentration, therefore it could be suggested that there are acidic activation domains on the PHO2 protein. Acidic amino acid rich region of 287-326 aa in PHO2 is not a transcriptional activation domain. PHO2 maintained its activation activity only if Ser230 is phosphorylated, thus the phosphorylated site may play a key role in the transcriptional activation function of PHO2. PHO4 fused to the GAL4 DNA-binding domain also activates the expression of lacZ. A segment of 1-97 aa at its N-terminal is responsible for the transcriptional activation activity. A two-hybrid assay reveals that there exists interaction between PHO2 and PHO4 protein, and the interaction affects their transcriptional activation function.