SIGNAL-TRANSDUCTION BY MAP KINASE CASCADES IN BUDDING YEAST

Budding yeast contain at least four distinct MAPK (mitogen activated p rotein kinase) cascades that transduce a variety of intracellular sign als: mating-pheromone response, pseudohyphal/invasive growth, cell wal l integrity, and high osmolarity adaptation. Although each MAPK cascad e contains a conserved set of three protein kinases, the upstream acti vation mechanisms for these cascades are diverse, including a trimeric G protein, monomeric small G proteins, and a prokaryotic-like two-com ponent system. Recently, it became apparent that there is extensive sh aring of signaling elements among the MAPK pathways; however, little u ndesirable cross-talk occurs between various cascades. The formation o f multi-protein signaling complexes is probably centrally important fo r this insulation of individual MAPK cascades.