Models integrating functional elements of Secteur expression in Nectria haematococca. (A) First model: In the wild-type strain, the product of the SesA and SesB genes can exist in a normal state (AN and BN) and in a modified state (AS and BS). AS determines overproduction of pigments and BS is responsible for growth alteration. (B) Second model: The product of SesA, SesAp, is responsible for pigmentation. The product of SesB, SesBp, has a catalytic activity necessary for the normal growth. These two products negatively regulate each other, and the equilibrium constants favor SesAp. In juvenile thalli, only SesBp is produced, but SesAp can be randomly produced, switching to a new state with a majority of SesAp.