Evolutionary conservation of domain-domain interactions

Table 2 DDI-PPI mapping: interactions involving only single-domain proteins

Organism^a	E. coli	yeast	worm	fly	human
Number of PPIs (with known domains) (N)	497	2,418	335	2,068	1,633
Number of PPIs to which DDIs could be mapped (n) (%; n/N*100) Median value of random networks (P value)	117 (24%) 92 (0.005)	284 (12%) 79 (<0.001)	60 (18%) 38 (<0.001)	217 (10%) 55 (<0.001)	400 (25%) 135 (<0.001)

^a Organism labeling: yeast: S. cerevisiae, worm: C. elegans, fly: D. melanogaster. For the analysis of each organism, DDIs in the structural database that are based on single-domain proteins of the respective organism were excluded. DDI, domain-domain interaction; PPI, protein-protein interaction.

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