Ptc1 is a type Two C phosphatase involved in the mating decision of yeast. Ptc1 competes with Fus3 for control of the 4 phosphorylation sites on the scaffold protein Ste5. Presence of the mating pheromone α-factor causes Ptc1 to be recruited to Ste5. This recruitment takes place via a 4 amino acid motif in the Ste5 phosphosites.