Regulation of alpha-factor production in Saccharomyces cerevisiae: a-factor pheromone-induced expression of the MF alpha 1 and STE13 genes.

Production of the mating pheromone alpha-factor was examined in Saccharomyces cerevisiae MAT alpha cells that had been exposed to the mating pheromone a-factor. A 2-h treatment with a-factor caused a significant increase in alpha-factor concentration in the medium as demonstrated by a halo assay. MF alpha 1 is one of the two genes coding for a precursor of alpha-factor. A Northern (RNA) analysis of total RNA from a-factor-treated MAT alpha cells revealed a rapid two- to threefold increase in MF alpha 1 transcript levels, reaching maximum within 60 min of exposure to the pheromone. Pheromone induction did not require ongoing protein synthesis. a-Factor-induced MF alpha 1 expression was quantitated by analysis of an MF alpha 1::SUC2 fusion gene whose product was assayed for invertase activity. Expression of the MF alpha 1::SUC2 gene in MAT alpha cells responded to the a-factor signal like the chromosomal version of MF alpha 1. Maturation of the alpha-factor precursor involves three proteolytic activities which are encoded by the KEX1, KEX2, and STE13 genes, respectively. Two of these genes, namely, KEX2 and STE13, were examined for pheromone-induced expression. Only the STE13 gene exhibited pheromone induction at the transcriptional level.