FIGURE 2: Model of the asymmetric diversification of two mating pheromones in terms of specific proteases. M-factor is recognized by the Map3 receptor, leading to ‘bilateral' coevolution. By contrast, P-factor is recognized by both the Mam2 receptor and the Sxa2 protease, perhaps leading to ‘trilateral' coevolution coupled with P-factor divergence, thereby facilitating more rapid diversification of P-factor relative to M-factor.