A schematic description of the analysis. (a) A list of experimentally determined PPIs is compiled for each of the five organisms (E. coli, S. cerevisiae, C. elegans, D. melanogaster, and H. sapiens) from INTACT , DIP , and BIOGRID . (b) A list of structurally derived DDIs is compiled from 3DID  and iPfam  databases. (c) The appropriate domains are assigned to each of the interacting proteins according to the definitions of the InterPro database . (d) Based on the data complied in panels b and c, DDIs are mapped onto PPIs. (e) A list of PPIs with DDI assignments is compiled. (f) A list of the DDIs mapped onto PPIs is compiled. DDI, domain-domain interaction; PPI, protein-protein interaction.