Pheromone response, mating and cell biology.

Saccharomyces cerevisiae responds to mating pheromones by activating a receptor-G-protein-coupled mitogen-activated protein kinase (MAPK) cascade that is also used by other signaling pathways. The activation of the MAPK cascade may involve conformational changes through prebound receptor and heterotrimeric G-protein. G beta may then recruit Cdc42-bound MAPKKKK Ste20 to MAPKKK Ste11 through direct interactions with Ste20 and the Ste5 scaffold. Ste20 activates Ste11 by derepressing an autoinhibitory domain. An underlying nuclear shuttling machinery may be required for proper recruitment of Ste5 to G beta. Subsequent polarized growth is mediated by a similar mechanism involving Far1, which binds G beta in addition to Cdc24 and Bem1. Far1 and Cdc24 also undergo nuclear shuttling and the nuclear pool of Far1 may temporally regulate access of Cdc24 to the cell cortex.