Conservation of target sites. Distributions of branch lengths of target sites are illustrated (see main text for a definition of branch lengths). Shaded regions indicate the maximal branch lengths of target sites conserved in primates, in primates and rodents, in mammals, and in vertebrates. All cellular microRNAs considered here are conserved in vertebrates. Constitutive target sites of these microRNAs are significantly more conserved (P < 0.00304, two-sided Kolmogorov-Smirnov test) than context-dependent target sites. Moreover, neither context-dependent nor constitutive target sites of viral microRNAs show evidence for evolutionary conservation (see also Supplemental Fig. S7).
