FIGURE 5 

Network analysis. (A) Topology measures (first column, see text for definitions) for each color-coded level, active, and inactive regulators (first row). (B, C) Network robustness. Sequential attacks against TFs cause the characteristic path length to rise (B) as connectivity decreases (C) until the network reaches a breakdown point (peaks in panel B). TF attacks cause the connectivity of the TF subnetwork to disintegrate more rapidly than the overall transcriptional network, without affecting communication within other regulatory levels (flat lines). (D) Network adaptivity. In contrast to inactive genes, increased communication between regulators at active genes expedites the propagation of information (compare average neighboring levels and characteristic path length of last 2 columns in panel A) and may improve the speed and redundancy of the cell's response to dynamic environmental conditions. Our unified model connects several factors individually implicated in active gene expression (Lieb et al, 2001; Casolari et al, 2004; Robert et al, 2004).