Identification of hierarchical and modular nodes. (a) Distribution of the clustering coefficient, C(k), and calculated κ value. The blue line represents the C(k) power law. The dashed red line indicates the κ value obtained for this C(k) distribution. Red triangles represent hierarchical nodes, while green circles indicate modular nodes. (b) The characteristic path length after cumulative removal of all hierarchical nodes and some modular ones. The red dashed line indicates the sudden change in the original increasing tendency when the last hierarchical TFs (FlhDC and Fur) were removed. This suggests that the removal of hierarchical nodes broke the connections bridging modules, thus disintegrating the TRN.