over-expression of Ppz1 is deleterious for yeast cells. Recent studies in our laboratory demonstrated that the over-expression of a catalytically impaired version of Ppz1 (Ppz1R451L) is not toxic, suggesting that the excess of Ppz1 phosphatase activity was responsible for toxicity, possibly due to changes in yeast phosphoproteome [1]. Because the molecular basis of this toxicity are still unknown, a global yeast phosphoproteomic assay was designed to gain insight into this phenomenon.