Fig. 1.
Model of protein evolution that couples biophysics and population dynamics in the polyclonal regime. (A) A model of organism composed of ten genes from the folate biosynthetic pathway (supplementary table S1, Supplementary Material online). Cellular fitness f is proportional to the effective metabolic output of this pathway and the total number misfolded proteins (eqs. 1–3). The population is subject to mutation, drift, and purifying selection. Mutations can change the folding stability ΔG of a gene and hence the fitness of the cell (see Materials and Methods). Effective population size is Ne = 103. (B) Fitness under mutation–selection balance. (C) Detailed trajectory of the folding stability of each gene in individuals in the population. Individual cells are indexed along the y axis, where spatial proximity is proportional to kinship.