Substitution rate of translation initiation signals. The Y axis shows the change rate between TA signal and SD signal usage. The X axis shows the evolutionary distance of 16S rRNA. Each black point denotes an Actinobacterial genome, and all the distances are calculated by comparing with Streptomyces Coelicolor A3(2); each red point denotes a genome in Streptococcaceae, and the distances are calculated by comparison with Streptococcus pyogenes M1 GAS. The linear regressions are y = 0.04+1.61x (black line, R = 0.77) and y = -0.03+1.67x (red line, R = 0.77), both with p-value < 0.0001.