The isolation of biologically active mating pheromone, a-factor, from the yeast, Saccharomyces cerevisiae

Haploid cell-types of baker's yeast, Saccharomyces cerevisiae, secrete pheromones which are essential for conjugation. Recently a putative structure for the elusive a-factor pheromone has been reported. In this report we present a procedure to obtain a-factor from batch cultures of cells using hydrophobic Amberlite XAD-2 resin in the growth medium with subsequent differential washings of the resin with organic solvents. We have determined the biological activity of the a-factor preparation by verifying that there is an increase in transcription of the a-factor receptor gene, STE3, by Northern analysis of STE3 mRNA before and after exposure of the appropriate cell type to a-factor. Furthermore, a beta-galactosidase assay of the putative receptor gene fused to the lacZ gene, coding for beta-galactosidase (STE3-lacZ), was done to quantify the biological activity of the a-factor.