FIGURE 2 

Predicting physically associated proteins from patterns of conserved co-expression. (A) Distribution of mRNA co-expression patterns of 1769 pairs of proteins that physically associate; (B) the distribution of co-expression patterns of 642 295 protein pairs that are not known to physically associate. By comparing the two distributions, we identify patterns that indicate the tendency to physically associate. In all panels, the x axis indicates the correlation of mRNA expression profiles of human gene pairs and the y axis the expression correlation of corresponding ortholog pairs in C. elegans. In (A, B), the z axis (represented as contours from purple (low) to red (high); white indicates zero) indicates the fraction of human gene pairs in either the true-positive (A) or -negative (B) set having a correlation 'x' with C. elegans orthologs having a correlation 'y'. (C) Log likelihood that human protein pairs with a given conserved co-expression pattern will physically interact, calculated as the logarithm of the ratio of the two distributions, corrected by prior expectation, and ranging from blue (negative) to red (positive) is plotted; white indicates zero. Contours are labeled with values of the log likelihood score.