We analyze the human PPI network of Radivojac et al. that contains 41,456 physical interactions between 9,141 proteins [28] , as well as the human PPI networks from BioGRID [24] , that contains 30,513 physical interactions between 8,581 proteins, and from HPRD [23] , that contains 36,811 physical interactions between 9,449 proteins (we downloaded them in June 2010). Since we obtained qualitatively similar results for all three networks, for simplicity we report only on the PPI network of Radivojac et al. [28] ; we chose this network, since it has the largest number of interactions.