The alpha factor pheromone arrests yeast in the G1 phase of their cell cycle, this allows the opposite mating type cells to synchronise. Alpha factor mating pheromone induces the expression of mating genes, changes in nuclear architecture, and polarizes growth toward the mating partner. STE2 encodes the alpha factor pheromone transmembrane G-protein coupled receptor (GPCR) found on mating-type-A cells in yeast. Alpha factor binds Ste2 and activates prototypic mitogen-activated protein kinase (MAPK) cascade. The dose of pheromone exposure differentially activates the MAPK Fus3 for alternate effects. A high dose of alpha factor leads to growth arrest and schmooing formation for mating; a lower dose causes elongated cell growth.