The networkof post-translational modifications (phosphorylation/dephosphorylation, proteolytic cleavage, etc.) of human proteins shown here includes 1671 automatically and manually curated edges between 732 proteins. listed in the ResNet 4.0 database. The hierarchical layout shown here is generated by our simulated annealing algorithm. Green arrows represent hierarchical links while red arrows – 208 anti-hierarchical (putative feedback) links going from lower to higher (or the same) levels in the hierarchy. Only proteins and links reachable from one of the 71 receptor-proteins placed at the top hierarchical level were included.