Figure 1

Inferring interactions by homology. Each interaction is inferred from homology to experimentally observed interactions. In this schematic, proteins a ₁ and b ₁ have been shown experimentally to interact in one organism, here labelled 'species X', and protein a ₂ and b ₂ in another, 'species Y'. Lists of homologues are generated for each of the proteins, ranked by their bit score ($s_{a_i}$, $s_{b_i}$, etc.). A protein from one list may interact with a protein from the other (shown by the red arrow) and potential pairwise interactions are scored according to Equation 1, based on homology to the proteins involved in the known interaction. Furthermore, interactions receive a higher score if they are derived from multiple experimental sources (n > 1). The score is additive, for instance, in the example here, the blue and green sequences are predicted to interact based on the interactions in 'species X' and 'species Y' and the overall score is the sum of both pairwise scores. This additive process continues over all experimentally determined protein pairs, N, (e.g. through 'species Z'), for which the rat sequences, labelled blue and green, are present.