Courtship in S. cerevisiae: Both cell types choose mating partners by responding to the strongest pheromone signal

We demonstrate that during the courtship stage of conjugation, S. cerevisiae a cells choose the α cell producing the highest level of pheromone from among potential mating partners. From this result and that for α cells we conclude that both a and α cells act as signaling cells during courtship, that both cell types respond by discriminating different levels of signal, and that the signals are the mating pheromones. Responding cells that are supersensitive to signal fall to discriminate pheromone-producing from nonproducing cells to an extent that depends on their degree of supersensitivity. We propose that partner selection in S. cerevisiae results from polarized morphogenesis of a responding cell in the direction of highest pheromone concentration and that cells defective in discriminating this gradient execute a default pathway in which an adjacent cell is selected at random.