Yeast PHO2 protein plays a role in the expression of several different genes and acts as a multiple global activator. Here we report the comparison of the effect of PHO2 protein on the expression of PHO5, HIS4 and Ho genes. In the PHO2 defective yeast strain, PHO5 gene could not be depressed in low Pi and the expression of the HIS4 and HO genes was decrease to 25% and 40% of the normal level respectively. When the PHO2 gene carried by low copy shuttle vector was transformed into this strain, the expression of the three genes could be restored. Previously the PHO2 gene was mutated on its conspicuous regions with site-directed mutagenesis, deletion and linker insertion. Here the effects of these mutations on these genes were compared.