Signal transduction and growth control in yeast.

An understanding of how an extracellular stimulus causes changes in cell growth is emerging from the study of four signal transduction pathways in Saccharomyces cerevisiae: the pheromone-response, pseudohyphal differentiation, osmolarity-response, and protein kinase C activated pathways. Each of these pathways contains at its core a distinct mitogen-activated protein kinase cascade. Biochemical and molecular studies have determined the functional order of the kinases in the pheromone-response pathway and have suggested that they are organized into a complex by a protein scaffold. The cell surface sensor system for the osmolarity-response pathway has been identified. It shows striking similarity to bacterial two-component sensor-responder systems. Finally, components that integrate information from these pathways and communicate it to cell growth regulators have been revealed.