Pheromones and Pheromone Receptors Are the Primary Determinants of Mating Specificity in the Yeast Saccharomyces Cerevisiae

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Saccharomyces cerevisiae has two haploid cell types, a and α, each of which produces a unique set of proteins that participate in the mating process. We sought to determine the minimum set of proteins that must be expressed to allow mating and to confer specificity. We show that the capacity to synthesize α-factor pheromone and a-factor receptor is sufficient to allow mating by matα1 mutants, mutants that normally do not express any α- or a-specific products. Likewise, the capacity to synthesize a-factor receptor and α-factor pheromone is sufficient to allow a ste2 ste6 mutants, which do not produce the normal a cell pheromone and receptor, to mate with wild-type a cells. Thus, the a-factor receptor and α-factor pheromone constitute the minimum set of α-specific proteins that must be produced to allow mating as an α cell. Furthermore, the production of these two proteins dictates the mating specificity exhibited by that cell. Further evidence that the pheromones and pheromone receptors are important determinants of mating specificity comes from studies with matα2 mutants, cells that simultaneously express both pheromones and both receptors. We created a series of strains that express different combinations of pheromones and receptors in a matα2 background. These constructions reveal that matα2 mutants can be made to mate as either a cells or as α cells by causing them to express only the pheromone and receptor set appropriate for a particular cell type. Moreover, these studies show that the inability of matα2 mutants to respond to either pheromone is a consequence of two phenomena: adaptation to an autocrine response to the pheromones they secrete and interference with response to α factor by the a-factor receptor.

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