Interaction and Reaction Systems (IRS) for the Leloup and Goldbeter's model. Interaction and Reaction Systems for the Leloup and Goldbeter's model where the labeled arrows are interactions (positive (+) or negative (-)) and where the non-labeled arrows are reactions. The left part represents the IRS. The right part represents the IRS after simplification where P
stand for the total of proteins PER and TIM, as used in our analysis.