Degree of overlaps between randomly selected protein interaction pairs in selected protein interaction databases and MetaGene pairs. We randomly selected 1,000 protein-protein interactions, and counted the numbers of protein interaction pairs overlapped with conserved co-expression pairs in the MetaGene database. This sampling and MetaGene overlapping process was repeated 1000 times for each protein interaction database (including the random database). The resulting distributions of overlaps are show as profiles on the graph. 3A. Comparisons of Metagene overlaps for major human PPI databases, including: HAPPI, OPHID, ProNet, BioGrid, and IntNetDB, and HAPPI 4-star subset. 3B. Comparisons of Metagene overlap for different quality grade subsets of the HAPPI database, including: HAPPI (all), HAPPI 2-star, HAPPI 3-star, HAPPI 4-star, and HAPPI 5-star subsets. There are 6145 co-expression pairs in MetaGene database in total. And there are 22154 PPIs in HAPPI, HPRD etc. The x-axis represents the number of overlap protein pairs in HAPPI and MetaGene when we random selected 1000 PPIs. The scale of x-axis is calculated as 1/((6145/22154)*1000).