Budding yeast mating is an excellent model for receptor-activated cell 
differentiation. Here we identify the related transcription factors Ecm22 and 
Upc2 as novel regulators of mating. Cells lacking both ECM22 and UPC2 display 
strong mating defects whereas deletion of either gene has no effect. Ecm22 and 
Upc2 positively regulate basal expression of PRM1 and PRM4. These genes are 
strongly induced in response to mating pheromone, which is also largely 
dependent on ECM22 and UPC2. We further show that deletion of PRM4 like PRM1 
results in markedly reduced mating efficiency. Expression of PRM1 but not of 
PRM4 is also regulated by Ste12, a key transcription factor for mating. STE12 
deletion lowers basal PRM1 expression, whereas STE12 overexpression strongly 
increases PRM1 levels. This regulation of PRM1 transcription is mediated through 
three Ste12-binding sites in the PRM1 promoter. Simultaneous deletion of ECM22 
and UPC2 as well as mutation of the three Ste12-binding sites in the PRM1 
promoter completely abolishes basal and pheromone-induced PRM1 expression, 
indicating that Ste12 and Ecm22/Upc2 control PRM1 transcription through distinct 
pathways. In summary, we propose a novel mechanism for budding yeast mating. We 
suggest that Ecm22 and Upc2 regulate mating through the induction of the mating 
genes PRM1 and PRM4.