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

Abstract 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 β-galactosidase assay of the putative receptor gene fused to the lacZ gene, coding for β-galactosidase ( STE3-lacZ ), was done to quantify the biological activity of the a -factor.