Table I.

Sources of protein-protein interaction data

Database	# interactions	# proteins	# species	Data source	Reference #	Date Downloaded
DiP	57,683	20,728	274	Literature curation	37	Aug., 2009
Entrez Gene	387,159	19,205	unknown	Linkout databases	38	Sep., 2009
HPRD	38,806	27,081	1	Yeast 2-hybrid, in vitro or in vivo experiments, Proteinpedia	39	Aug., 2009
MINT	83,321	29,774	unknown	Literature curation	40	Jun., 2009
Virus MINT	1,854	468	99	Literature curation	23	Nov., 209
IntAct	216394	63654	unknown	Experiments	22	Jun., 2010
Total	785217

^*Total does not consider that different databases may use different accession numbers for the same protein.