Dependency of ω = dN/dS on protein core size and expression level. (A) Core size affects evolutionary rate on the surface of the protein but not in the core. (B) Expression level affects evolutionary rate both on the surface and in the core. However, it has a bigger effect on the surface of the protein. In both figures, the solid lines were estimated jointly from the data using a linear dependency of ω on RSA. Points for individual bins are shown for illustration purposes only. They were estimated using a per-bin model for ω. The dashed black line represents the genome-wide trend, as shown in Figure 2, and is provided as a reference.