These are integrators of molecular signals coming from different sources, and regulated by the interconnections. cAMP may represent such a junction because it is affected in a positive or negative manner by a variety of signals. Phosphokinase A as a node may then split the signals and directs them to multiple targets such as the cytoskeleton and cellular traffic, gene expression and cell growth, metabolism, ion channels, G protein-coupled receptors of signal transduction, and neuronal synapsis. Another example of a node is Cdc42, which receives signals through receptor tyrosine kinases (RTK) and G protein-linked receptors (GPCR) and then sorts them into serum response factor (SRF) and p21 activated kinase (PAK), S6 kinase affecting transcription, translation and cellular traffic.  signal transduction,  Cdc42,  RTK,  G proteins,  PAK,  S6 kinase,  coordinate regulation; Jordan JD et al 2000 Cell 103:193; McCarty DR, Chory J 2000 Cell 103:201; Vohradsky J 2001 FASEB J 15:864.