Figure 4

Models for interpreting NNP and NPP configurations. A) The fraction of epistatic triplet motifs containing zero, one, two or three edges where the gene products physically interact varies significantly between motif types. Arising from this and other observations, two models are proposed. B) NPP: Two proteins play partly redundant roles in a pathway, while they both interact with a third protein that acts in an opposing or antagonistic role, typical of a regulator. Two pathway examples, one forked and one linear, are shown. C) NNP: Different protein complexes coordinate or modify their activities by communicating with each other, mostly likely via a direct or indirect interaction between the proteins that span the two complexes.