We show a tree constructed for one of the 335 families. The IL-6 (PF00489) family contains 10 viral proteins ( Figure 3C , blue) that are split to two sub-trees of viral clusters (VC) and other 136 Metazoan proteins (marked as collapsed sub-trees). The maximal depth in this tree is 19 (included in the collapsed sub-tree, red triangle). The deepest viral protein in the tree is of depth = 9, and its normalized depth is 9/19 = 0.474. The depth of the viral cluster (VC, the maximal sub-tree which contains all viral proteins) is therefore, 4/19 = 0.211.