The Petri net model of the mating pheromone response pathway of S. cerevisiae. The Petri net, modelling the signal transduction pathway of the mating pheromone response in S. cerevisiae. The meaning of the places is listed in Table 3 and of the transitions in Table 4. The logical nodes are coloured in grey. A logical node is identified by its name and exists in multiple copies in the net, which are logically identical. This construct is mainly used to avoid immoderate arc crossings. The transitions, which are contained in the seven MCT-sets of Table 5, are coloured differently.