1. Experimentally identified protein-protein interaction (PPI) data sets. 
2. These PPI data were taken from several predominant public databases, including BioGRID, HPRD, DIP, MINT and IntAct. 
3. Five organisms including Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster, Mus musculus and Homo sapiens were considered.
4. Data format: The 1st column, Interactor A; The 2nd column, Interactor B; The 3rd column, Source of PPI pair. 
5. All protein sequences in PPI data were mapped to the UniProt database.
6. Files:
(1) SC.exp.ppi: budding yeast PPIs
(2) CE.exp.ppi: nematode PPIs
(3) DM.exp.ppi: fruit fly PPIs
(4) MM.exp.ppi: mouse PPIs
(5) HS.exp.ppi: human PPIs
7. Last updated, April 10, 2010. 
