Emergent colinearity in a model of modular polyketide synthases

Polyketides are widespread, biologically active heteropolymers assembled by complexes of modular polyketide synthase(PKS) proteins. We implement a model of this system and explore its evolutionary behavior while subject to recombination in a changing environment. Under appropriate population parameters the combinatorial exploration of novelty allows a finite population to maintain high fitness indefinitely. Accompanying this maintenance of fitness is the phenomenon of emergent colinearity, a correlation between genetic order and the functional order of the product polyketide. Colinearity is a known characteristic of modular PKS systems. In our model it arises despite the absence of phenotypic effect. We understand this by observing that colinearity enhances the likelihood of recombination forming novel high-fitness phenotypes. We are able to quantify this effect, successive selective sweeps drive our evolving populations towards a fixed point in our colinearity parameter y. The existence and location of this fixed point is found to depend only on the density of states ρ(y) and the likelihood of recombination creating high-fitness