Nonspecific interactions between proteins could interfere with the functional specific complexes. The requirement to form specific complexes and avoid nonspecific interactions sets an upper limit on the protein diversity in a cell. Using the data from Yeast 2 Hybrid experiments, we obtain a quantitative description of the nonspecific protein interactions in yeast cells, and find the limit of protein diversity in the cytoplasm of yeast cells which allows for formation of mostly specific interactions. We find that the yeast cells have evolved to operate closely to the upper limit of protein diversity, and their protein concentrations are as low as possible to reduce the nonspecific interactions. In this way we reveal an insight into the experimental data of coexisting protein types as well as typical protein concentrations in yeast cell cytoplasm. This study has implication for our conceptual understanding of multicellulary and differentiation.