SIGNAL-TRANSDUCTION AND PROTEIN-KINASES - THE LONG WAY FROM THE PLASMA-MEMBRANE INTO THE NUCLEUS

All living cells must be able to receive information from the extracel lular space and to react to it by processing and converting it into in tracellular effects. If the properties of cells are to change in the l ong term, some signals must reach the nucleus in order to bring about changes in gene transcription. Three of the pathways, beginning with a n extracellular signal and ending with the nucleus, serve to illustrat e some principles of signal transduction such as signal conversion, si gnal cascade, cross-talk, and on/off switch. One element common to mos t of the pathways is the activation of protein kinases. One example of these kinases, the protein kinase C, is discussed as a vehicle of sig nal transport toward the nucleus and as a means of cross-talk between different signaling pathways.