Functional group predicted interaction. (A) Distribution of our predicted interactions in functional categories. Each axis on the matrix of protein density represents the yeast proteome, which has been subdivided into 13 functional categories. The width and the height of each cell, except for the “Uncharacterized,” which is too large to be shown in scale, is proportional to the number of proteins in the corresponding categories. (B) Comparison of cofunctionality index, which is defined as the ratio of the average protein interaction density for homofunctional interactions (diagonal of the matrix in A) to the average protein interaction density for heterofunctional interactions.