Effects of permanent and transient interfaces on protein evolutionary rate. Mean and standard deviation of protein evolutionary rate dN in the "SIN" dataset are shown for non-co-expressed proteins with single interface (NC-S, in a total of 10 proteins), non-co-expressed proteins with multiple interfaces (NC-M, in a total of 12 proteins), co-expressed proteins with single interface (C-S, in a total of 10 proteins) and co-expressed proteins with multiple interfaces (C-M, in a total of 51 proteins). C-M evolve significantly more slowly than NC-S (P = 1.05e-02), NC-M (P = 1.34e-02) and C-S (P = 2.29e-02). Other comparisons did not yield significant results (i.e., P > 0.05). P is calculated by one-sided Wilcoxon rank sum test.